Increase in low-birth-weight infants in Japan and associated risk

Transcription

J. Obstet. Gynaecol. Res. Vol.３１, No.４; 314-322 August 2005
Increase in low-birth-weight infants in Japan and
associated risk factors, 1980-2000
Hldemi Takimoto, Tetsuji Yokoyama Nobuo Yoshiike and Hideoki Fukuoka
Departments of Health Promotion and Research, Section of Maternal and Child Health, and Technology Assessment and
Biostatistics, National Institute of Public Health, Saitama, Division of Health and Nutrition Monitoring, National
Institute of Health and Nutrition and Department of Developmental Medical Science, Division of International Health,
Tokyo University Graduate School of Medicine, Tokyo, Japan
Abstract
Ainl: To investigate possible factors related to the recent rise in pre¥'alence of low-birth-weight (LBW) infants
in Japan.
Methods: A data set comprising 11 746 infants frorn the Children and Infant Growth Surveys (1980, 1990, and
2000) was analyzed.
Results: The proportion of LBW infants was 4.2"/ in 1980, 6.1*/* in 1990, and 8.3*/. in 2000. The maternal smoking prevalence increased from 6.5"/. in 1990 to 10.9'/ in 2000. When multivariate logistic regression analysis
was applied to estimate the risk for LBW from 1990 to 2000, the following were selected as independent factors: preterm delivery, early term delivery, female sex of the infant, maternal primiparity, multiple gestation,
maternal short stature, older maternal age (>24 years), and maternal srnoking. The population attributable
fraction (PAF) of preterm plLIS early terrn delivery and multiple gestations to LBW was 85.1'/. in 1990, and
89.3"/. in 2000. Tl"le PAF of maternal srnoking was 6.4'/. in 1990, and 7.4"/. in 2000.
Conclusions: The increase in preterm deliveries and multiple gestations were found to be the important
factors with regard to the increase in LBW infants in Japan. The increased pre¥'alence of rnaternal smoking
was not substantially associated with the increase in LBW infants.
Key words: health survey, infant, Iow birth weight, multiple pregnancy, premature birth
Introduction
tively, in 1980, but has increased to 7.80/0 and 9.5"/o,
respectively, in 2000. Preterm delivery at <37 weeks'
The mean birth weight in Japanese infants steadily
gestation has also increased from 4.1*/o in lc)80 to 5.4'/o
increased after World War II, reaching a peak value of
3.24 kg for boys and 3.15 kg for girls in 1974. Since
then, the mean birth weight has been declining: from
USA, Canada,2 Sweden3 and Norway,4 have experi,-
3.23 kg for boys and 3.14 kg for girls in 1980 to 3.07 kg
for boys and 2.99 kg for girls in 2000. The prevalence
rate of low-birth-weight (LBW) infants (birth weight
<2500 g) has also increased during this period: the
rate for boys and girls was 4.8'/. and 5.6"/., respec-
in 2.000.1 Other industrialized countries, such as the
enced an opposite trend during the same period: the
mean birth weight had increased and the prevalence
of LBW has declined.
LBW infants, are known to be at risk of increased
mortality,5,6 and also of developing chronic diseases
such as ischemic heart disease and diabetes in later
Rece'ivc'd: SePtc'mber 2L) 2OO4.
Accepted: APril 22 2OOr'*.
Repr'int reLlu(?h.'t t()' l)r I IiLiL,mi Takimoto. Section of Maternal and Child Hea]th. Department of Heaith promoti()n clnd Research,
Nation 11 11lhtitutL, ()F l'Llblic Health, 2-3-6, Minami, Wako-City, Saitama Pr 'fectule 3510197 Japan Email tllldt:1111@l Ph o Jp
- 1 96 -
Inc_rease in low birth weight in Japan
life.710 The recent increase in LBW infants in Japan
sus unit, under the supervision o_ f the municipal gov-
might impose a soc_ial burden in the future.
ernments. The survey participants were requested to
attend the routine infant health examinations at the
centers in charge of the survey The weight, height,
head circumference, and chest circurnference of all
infants were measured by trained public-health nurses
according to the measurement protocol pro¥'ided by
Despite this deteriorating trend in maternal and
child health statistics, Iittle attention had been paid to
this issue by health professionals in Japan, and published reports are scarce. This is probably due to the
extreme lowness of infant mortality rates in recent
years, which have declined from 7.5 per 1000 Ii¥'e
the Ministry of Health. L,abour and Welfare.13 Informa-
births in 1980 to 3.2 in 2000.1 To date, there are only two
tion on infant sex, birth weight, birth height, gesta-
reports focused on changes in maternal and child
tional length (weeks) and maternal age at delivery,
birth order, and the number of gestations in the same
health risks in Japan. From birth record analysis in
Tokyo Metropolitan Hospitals, Yoshimura and Kato
reported a secular dec_1ine in mean birth weight from
1979 to 1989,l Ohmi et al. have hypothesized that an
increase in the prevalence of smoking and a decrease in
body mass index (BMI) in young women could be
related to the increase in LBW infants.12 However, no
systematic evaluation has been carried out nationally
The Children and Infant Growth (CIG) Survey is a
national Japanese sur¥rey on anthropometric parameters (weight, height, head circumference, and chest circrurlference) in children between O and 6 years old, and
it has been carried out every 10years since 1950.13
InfonTtation on the birth status of infants and maternal
background has also been recorded in this SLlrveY
In order to: (i) identify the possible underlying
factors causing the recent rise in LBW Jap.anese in-
pregnancy was obtained from copies of the birth
records, which was kept in the Maternal and Child
Health Handbook (Boshi-techo) by the obstetrician or the
midwife. All events during pregnancy and delivery
and postpartum are recorded in this handbook, which
is given to every pregnant woman in Japan by their
10cal municipality Information on maternal, height
and self-reported smoking habits during pregnancy
was assessed in the 1990 an 2000 surveys. Maternal
prepregnancy weight and frequency of alcohol drinking (times per week) were assessed only at the 2000
survey: We defined 'drinkers' as mothers who reported
drinking three or more times per week,
A total of 43 082 infant-mother pairs was identified
during the three survey periods (1980, 1990, and 2000).
Total participation rates in the survey were 93.50/. in
fants; and (ii) suggest possible means for the reduction
1980, decreasing to 90.9'/o in 1990, and to 81.40/. in 2000.
of the rate of LBW, we analyzed the data sets of the
CIG surveys obtained in 1980, 1990, and 2000.
In order to compare our results with the vital statistics
Materials and Methods
data, we limited our dataset to infants your ger than
12 months. A total of 11 746 infants whose complete
birth status record was available v¥'ere used for this
anal ysis.
We used the data sets from the CIG surveys carried out
by the Ministry of Health, Labour and Welfare in 1980,
1990, and 2000.13 This survey consists of two sets of
One-way ANOVA Was applied to continuous vari-
data from the population-based and hospital-based
ables to compare the data from the three surveys. A
t-test was applied to compare continuous variables
between two survey periods. Chi-squared tests were
survey, In the current study, the data sets frorn the pop-
used for comparing proportions of selected categories.
ulation-based survey were used with the permission
of the authority; the Ministry of Health, Labour and
To estimate the factors related to the birth of LBW
Welf are.
The participants in the population-based survey
were selected through a two-･step sampling method.
All children from the age of 2 weeks to 2 years were
recruited from 3000 randomly selected census units
defined by the Ministry of Health, Labour, and
Welfare.13 In order to recruit children aged 2-5 years,
infants, Iogistic regression analysis was applied. The
population attributable fraction (PAF) of selected fac-
tors to LBW was calculated using the following equation,14 where ni is the number of LBW in the ith risk
category, RRi is the relative risk (odds ratio [OR]) in the
ith risk category (RR = I in the referent category).
PAF = I -
(ni / RRi)
n, ,
750 census units (900 in the 2000 survey) were rando
mly selected frorrL the above 3000 census units.
The population-based survey was carried out at
loc_al public health centers located in the selected cen-
A P-value of <0.05 (two tailed) was considered to be
significant. All statistical analyses were carried out
using the statistical package. SPSS (version 11.SJ).
- 197-
H. Takimoto et al.
Results
40
The general characteristics of the survey participants
according to survey year are shown in Table I . The
data from the vital statistics report in Japan for each
survey year are shown together with the survey data.
The changes in infants over the 20-year period of the
CIG survey were characterized by a significant
decrease (IJ < 0.01) in mean birth weight, height, and
.' 30
eJ)
c
: !
o
(,,
20
o
u
F:
(L)
*
(L)
r ;
>
(V
10
cu
6.40/0
7.40/06.00/0
gestational length. LBW (<2500 g), very low-birth-
weight (VLBW; <1 500 g), preterm deliveries
o
(<37 weeks' gestation), early preterm deliveries
<20 years
2 o24
25-29
Age (years)
(<32 weeks' gestation), and multiple gestations had
significantly increased (P < 0.01) during the 20-year
period. The proportion of high-birth-weight infants
( 4000 g) and post-term deliveries ( 42 weeks') had
3034
35
Figure I Smoking prevalence according to survey year
and maternal age category. *P < 0.01 between 1990 and
2000 (using chi-squared test). ([1) 1990, ( j) 2000.
significantly decreased (IJ < 0.01).
Changes in maternal anthropometry, age distribution, and smoking prevalence were observed. Mean
The proportion of short-statured mothers (<150 cm)
infants, both primiparas and multiparas, both multiple
and single gestations, both short-statured and normal
height mothers, in 30-34-year-old rnothers, and in non-
significantly decreased (P < O.O1). The mean inaternal
smokers.
age at delivery increased significantly (P < 0.01)
between 1990 and 2000. The proportion of both young
LBW, we compared the OR of LBW for each of these
rnaternal height had increased significantly (P < 0.01),
mothers (<20 years) and advanced-aged mothers
(>34 years) had significantly increased (P < 0.01). The
results from the CIG survey were quite similar to that
of the vital statistics data, except for the proportion of
VLBW and early pretenn deliveries. The proportion of
VLBW and early preterm deliveries was lower in the
survey group cornpared with the vital statistics data
for the three survey periods, but had significantly
In order to examine the effect of selected factors on
factors by applying univariate logistic regression analysis, and estimated their PAF for the three survey peri-
ods (Table 2). The OR for LBW in preterm and early
term infants were significantly higher (P < 0.01) compared with full-term infants (40 1 weeks) in all three
survey periods. The OR for LBW in preterm and early
term infants increased over the 20-year period. The OR
for LBW in multiple gestations were significantly
increased (P < 0.01) in parallel with the national data.
higher (P < 0.01) compared with single gestations, and
The prevalence of maternal smoking during preg-
the values increased over the survey period. The OR
nancy increased significantly from 1990 to 2000, and
of LBW in short-stature mothers was also significantly
the median number of cigarettes smoked by smokers
higher (P < 0.01) compared with normal-statured
increased frorn seven per day in 1990 to 10 per day in
2000 (P < 0.01 using Mann-Whitney U-test). The smok-
mothers, but the values rernained stable over the 20-
ing prevalence in 5-year age groups for each survey
period (1990 and 2000) are presented in Figure 1.
The youngest age group showed the highest smoking
age on LBW in the 1990 survey, but the OR of LBW was
high in both young and older mothers in the 2000 survey. When subjects were grouped according to quartiles of maternal prepregnancy BMI, the OR for LBW
was 1.70 (95"/* confidence interval [CI] = 1.03-3.09,
P < 0.01) in the lowest BMI category, compared with
the highest BMI category group. The OR for LBW was
2.03 (95"/* CI = 1.31-3.16, P < 0.01) for smokers compared with non-smokers in the 1990 survey, but not in
prevalence for both survey periods. Smoking prevalence was significantly increased (P < 0.01) in 2000 in
mothers 20-29 years old.
To examine the change in LBW prevalence according
to each factor, the proportion of LBW was calculated
for the three survey periods, after excluding post-term
infants. As shown in Table 2, the proportion of LBW
increased significantly (P < 0.01) during the 20-year
period among preterm infants, early term infants from
37 to 39 weeks' gestation, both female and male
year period. There was no significant effect of maternal
the 2000 survey The PAF for LBW was notably large
for shorter gestational length, multiple gestation, both
young and advanced age at delivery, and low prepreg-
nancy BMI.
･･- 1 98 -
Increase in lovv birth weight in Japan
t¥
Lr)
o
o
*H
*H
oo li
O
cr)C: .
OOO
Cf)
OC
j
OO
a (I iI Oa¥
Cc;l ,H
** I
eo
¥ot¥H
ooO*H
Lr;c;c;
cf).Lr).(
Lr).¥O,1)
1 1 l
l)
'
,
O
(Q) 1
,H
oO
(/) Lr)
UH
+* crH
l
tr)
u) c l
'C;!OIH
Ii
O
eO
O
Cf)l
(/)C?¥ :
-s rH -
.
OOH
CC i C0606 ;
(
O･H
I I ! l
l
;
Q
oo
oO
O
t¥
Lr)
H
*+0
ooo ll
( l o
CP
(S H
LrS (::; c
ri(f:J
O (N H( C,
HLr) N
Fc
HHN l06
IC C5
I 1
1 l
ei
J)
(Is
c s>c:s
( ¥
Lr;
i c l *'
+1 +1
+ +1 +
cr)O O
v)>,oo ll
e)o
>; c
cf) Lr)
( lcf)t¥
t
Q
t¥
c l
0606
cf) cf)
l-
cr)¥Do
06dH
Qooo
oOLr)O
Lr C;
o¥c: oa
)oo
++
t ( 1
ot
+1 +1
(
o oo
c:s
oc} c:50
O
Q6c i h ( *HLr)( 10*+
rl
r
H
;
e'
e)
:;
.
O
c
*f o_ ll
, i
:
cf)cr)r
rl_.
Lr;
+ +1
(s ¥oooc;to 06cf)o Lr)
+ +1 +1
:
c l(S (
H
cf)
lr -
cr)
Hc
5C;oo
;
) )t
,* I
+c¥1+
+H
c 11H.Lr)
+ +1 +1
ooo ll
(S DLr)
O _*
cf) icr)
Lr)
ooT e O ;
rH -
+1
C IH(
o
Lr)Htr)
dC
c l,cf).L! Lr>.
Cf C5
'HO
e)
e)
E!
o::
o
u
LrS
C TH
U ¥O4
lQ
Q)
IHLr) oc O Hl I C;
( C:; ;
8
:; c l
(v
C *
o +cr)
( . i
H C¥1
*.
eO* QO
4'
oTHLr)
t H *H I I i I I I l
*
e
,
:
r;
' {
Cl)
HQJ
'
V
><
)t:(oo
aS
J:
V
'
Y*
C:*
) :oo
G) -
S
$:
CIS
(
-
Q)
+'
C:S
'
(o
._ __
o
:1:l
;
eO(/)
- -O-O
:;
O
H. H. (1S cQ
c f
S *(/) bOA p*V : (V
< Q)
V O Al
!SOC).
p*QJ
e,
S'::;
Q) a:lC ' c le)
: $:
eOeJO
'CV-iLF;CQ
* O (V-) i- v) (/)Hcl
Q C- _H ;- >. , ) ).
v) -H:1 ::,:Ir
･-,+' **:S :;.bJ0 ( l O
H
3 :_ .eJ)- : >(1'
O e) Q) .* * Q)cf)( C Q O
:
IH
Q;
'11
)'-'e)o
:(o q; .
HbJo
1
V)
{;
Q) ; o
;C¥1 G)
e;
e)
Lr)
D
>.
o o e;cf)V
?
H
(o '
o) <
Q)v ?p
c::;4:;
oo
) (o
OQ¥lrlQ)t *Su
OLr)b
)
--O
-bJ8 ) 0 cjt cf)V He'A : :oo, q) >.
>.S S!f!f> 9:v-c/)eO-,:; H(V
O
O
h
>._
> v) v)
) (ooo¥.._o
C1:S
H
U).; :o
;
C;
(Is
e,
r
:
- 199 --
P P (f)C
, {
c:s
(Is
:f
.ce
eO
'
*O
(f)
+
e)
H. Takimoto et a.1.
Table 2 Univariate logistic regression analysis for low birth weight, according to survey year
Variables
Survey
1980
No.
LBW/total ('/.)
OR
95*1*CI
PAF
('/ )
Inf ants
Gestational length
Preterm
86/190
(45.3)
Term
(37-39 weeks)
107/2511
(4.3)
Term (40 ;1 weeks) 27/2454 (1,1)
68.90
3.71
43.90-108.00
2.49 5.52
1 .OO
Ref erent
1 .28
0.98-1 .67
Ref erent
72.4
Sex
Female 114/2498 (4.8)
Male 101 12657 (3.8)
1 .OO
Mothers
Parity
None 10612057 (5.2)
1+ 114/3098 (3.7)
1 .44
1 . I O･--1 . 87
1.00
Ref erent
1.5
Pluralit y
Multiple 29/69 (42.0)
Single 191 /5086 (3,8)
Height
Short stature (<150 cm) 551747 (7.4)
l50 cm 165/4403 (3.7)
19.20
1 1 . 70-3 1 .40
1 .OO
Ref erent
0.93
0.92-0.95
2 . 04
1 .49-2 . 80
1 .OO
Ref erent
40.1
3.7
Age category (years)
<20
20-24
25-29
30-34
35
Prepregnancy body mass index (kg/nf)
18.99-20.30 -20.31-21.93
Smoking status
Smoker
Non-smoker
Drinking
Drinker
Non-drinker
Population attributable fractions (PAF) were calculated for variables significantly associated with low birth weight (LBW). -, Data not avail able; CI, confidence interval; OR, odds ratio.
In order to identify factors that could explain the
increase in LBW between the two recent survey peri-
dent factors with regard to LBW risk. After adjustment
for these factors, the survey period was no longer
ods (1990 and 2000), we applied the multivariate logistic regression analysis using the data set of 1990 and
related to the prevalence of LBW (OR = 1.05, P = 0.66
2000 surveys, as shown in Table 3. For both model 1
(using all variables) and for model 2 (applying the
stepwise method), preterm delivery, early term deliv-
P < 0,01) suggesting that these factors sufficiently
explained the increase in the LBW rate between the
1990 and 2000 surveys.
in model 1, whereas OR without adjustment = 1.37,
ery, female sex of the infant, maternal primiparity, mul-
The frequency of LBW among the combination
tiple gestation, maternal short stature, older maternal
groups of multiple gestation and gestational length for
age (>24 years), and maternal srnoking were indepen-
1990 and 2000 is summarized in Table 4. The PAF for
Increase in low birth weight in Japan
year of children and infant growth surveys
1990
No.
LBW/total ('/.)
OR 95･1.CI
2000
PAF
No.
( /*)
LBW/total ('/*)
83.5
103/161 (64.0)
ll7/1551 (7.5)
11/1051 (1.0)
731127 (57.5)
126/1953 (6.5)
125
67.5 232
6.39
3.72-10.9
15/1, 345 (1.1)
1 .OO
Ref erent
126/1682 (7.5)
88/1743 (5.0)
1 .52
1 . 15-2.01
l .OO
Ref erent
107/1432 (7.5)
99/1459 (6.8)
115/1966 (5.8)
1.16
O .88- I .52
1 .OO
Ref erent
106/1341 (7.9)
125/1422 (8.8)
30/56 (53.6)
184/3369 (5.5)
20.4
11.8-35.2
Ref erent
50.9
271230 (11.7)
187/3193 (5.9)
2,14
1 .39-3.28
6.1
1 .OO
Referent
2131 (6.5)
371542 (6.8)
85/1482 (5.7)
61/1045 (5.8)
291322 (9.0)
O.94
1.00
0.83
0.85
O.22 . I O
Ref erent
1 .35
0.81-2.24
1 .OO
124/1331 (9. .3)
2.50
O .56-1. .24
O.55-1 .29
2.03
1 .31-3. 1 6
l .OO
Ref erent
1 72
87.70-339.00
4.25-14.80
7.92
1.00
0.97-1,67
Ref erent
O.67-1 . 15
Ref erent
60/78 (76.9)
169/2669 (6.3)
49.9
28.80-86.40
1 .OO
Ref erent
201126 (15.9)
2.17
1 .32-3 .57
211 /2636 (8.0)
1 .OO
Ref erent
8/49 (16.3)
161376 (4.3)
82/1113 (7.4)
941907 (10.4)
31/314 (9.9)
4.37
1.7710.80
1 .OO
Ref erent
1 .78
1.033.09
1.51 .46
(9.6)
(l0.6)
(7,3)
(6.0)
6/39 (15.4)
22412712 (8.3)
1 .70
1 .88
87,0
Ref erent
1.27
1.00
2.59
2.46
PAF
("/.)
0.88
32/303 (10.6)
19912457 (8.1)
5.6
95*1.CI
1 .OO
671700
741701
511702
39/655
251222 (11.3)
189/3201 (5.9)
OR
75 .4
8.4
53.7
1 .37_-4 .58
1 . 1 3-2 ,57
31.4
1 . 26-2 , 82
1 .25
0.81-1.92
1 .OO
Ref erent
1 .36
O . 92-2 . O 1
1 .OO
Ref erent
2 . 05
0.85 i.93
1 .OO
Ref erent
each survey period were calculated by applying the
OR shown in Table 3 to these frequency data. The PAF
for LBW in multiple gestations and underterm deliv-
maternal age distribution was 37.50/0 in 1990 and 41 ,60/0
ery was 85,1"/. in 1990 and 89.3"/
Discussion
in 2000, clearly indi-
cating that the majority of LBW were attributable to
multiple gestations and under-term delivery In the
same manner, we also examined the effect of smoking
and maternal age distribution by using the data shown
in 2000.
The data from the CIG survey from 1980 to 2000 were
in Tables 3 and 4. The PAF for smoking alone was 6.4"/*
used to identify the underlying factors influencing the
recent rise in LBW Japanese infants, and to investigate
the c urrent risk factors for LBW. The increase in the
in 1990, and 7.6"/. in 2000. The PAF for smoking and
number of preterm deliveries and multiple gestations
- 201 -
H. Takimoto et al.
Table 3 Multivariate logistic regression analysis for low birth weight in the 1990 and 2000 surveys
Model 1
Variables
OR
Survey period (2000 vs 1990)
Model 2
P-value
95 1*CI
95'1 CI
P-value
79.80-207.00
4.38-10.20
<0.01
<0.01
0.66
0.83-1 .33
1 .05
OR
Inf ants
Gestational length (weeks)
Preterm
128.00
6.66
Term (37-39)
Term (40 1)
1.00
Female (vs male)
1 . 79
79.50-207.00
4.37-101.00
<0.01
<0.01
129.00
6.66
Ref erent
1 .41-2.26
1.00
1.78
Ref erent
<0.01
1 .41-2.26
<0.01
1 .62
1.27-2.08
12,30-30,30
1.21-2.76
<0.01
<0.01
<0.01
Mothers
Primiparity (vs rnultiparity)
Multiple gestation (vs single)
Short stature (vs normal stature)
19.30
1 .22-2.26
<0.01
<0.01
<0.01
0.95-5.22
0,07
2.26
1 .26-2.07
1 .62
19.20
12.30-30.20
1 .84
1 .83
Age category (years)
<2 O
2.23
20-24
25 29
1 .OO
1 .5'7
1 .07-2 . 03
3 O--3 4
1 .75
1 . 1 62.64
1 . 73
1 .06-2 . 8 1
2.19
1 .55-3 . 09
:35
Smoker (vs non-smoker)
Ref erent
Model 1: A11 variables were forced to enter into the model
1 .OO
0.02
0.01
0.03
<0.01
O.97-5.28
1 .77
1.07-2.31
1.18-2.66
1 . 74
1 .07-2 . 83
2.20
1.56-3.11
1.57
o.06
Ref erent
0.02
0.01
0.02
<0.01
Model 2: Significant variables were selected using the stepwise method.
CI, confidence interval; OR, odds ratio.
Table 4 Prevalence of low-birth-weight (LBW) infants according to selected factors
Combination of variables
Plurality
Multiple
Single
1990
No.
LBW/total
12/14
18/42
010
61/113
108/1911
15/1345
Preterm
Term (37-39)
Term (40 1)
Preterm
Term (40 1)
('/.)
LBW/total
36/38
24/38
012
661122
93/1505
1011042
94.7
63.2
0.0
4/15
26.7
16.1
8.9
3 1 79
3.8
10.8
13.6
15.8
11.8
4.4
85.7
42.9
54.0
5.7
1,1
0.0
54.1
6.2
1 .O
Age at delivery (years)
0/9
10/62
<20
20-24
25 29
30-34
7 1 79
6/48
2124
2122
271480
7811403
551997
271297
35
Non-smokers
No.
Gestational length (weeks)
Term (37-39)
Smoking
Smokers
2000
('/.)
Under 20
20-24
25-29
30-34
; 35
was found to be an important factor with regard to the
increase in the LBW rate. The increased prevalence of
maternal smoking and changes in maternal age distribution did not substantially explain the increase in
LBW infants in Japan.
The present study showed a consistency with prior
investigationsl5-17 regarding the relationship between
12.5
8.3
9.1
5.6
5.6
5.5
9.1
14/130
8/59
3/19
4/34
131297
68/982
86 /848
28 1 294
6.9
10.1
9.5
LBW and its risk factors. A11 of the factors shown in
Table 3, such as shorter gestational length, female sex
of the infant, maternal primiparity, both young and
advanced maternal age, and smoking, have been dernonstrated as risk factors for LBW.Is-17 However, the
temporary trend for an increased rate of LBW as a
result of increased preterm deliveries and multiple
- 202 -
Increase in low birth vveight in Japan
gestations is uniquely observed in Japan, while other
industrialized countries2 have experienc_ed a decrease
term infants compared with the vital statistics data
(Table l).
in LBW despite increased preterm deliveries and
Second, the information on maternal smoking and
multiple gestations.18 In these countries, an increase in
drinking habits was only obtained from self -report.
This might have led to under-reporting, as suggested
in former validation studies in pregnant women.21-23
fetal growth, particularly of term infants, has been
observed over time, which is attributed to increased
maternal size and decreased maternal smoking.
Why then, are Japanese infants born lighter despite a
decrease in short-statured mothers? The mean maternal height has also been increasing during the study
period, as shown in Table 1. This suggests that nutritional status was adequate irL these mothers during
their period of physical growth, but that it somehov¥'
deteriorated in adulthood. Through the analysis of
Third, important factors influencing pregnancy outcomes, such as prior obstetric history,24 weight gain
during pregnancy,25 maternal anemia.26 pregnancy
complications,27 and use of assisted reproductive tec_h-
nologres,28 were not assessed in this survey Lastly,
there was no information on whether the surveyed
infants were delivered spontaneously or not. Scheduled cesarean deliveries, Iabor inductio_ n, and indi-
25 years of anthropometric data in young women
cated preterm deliveries29 are known to affec_t
(aged 15-29 years), we observed an increase in the pro-
gestational length, and therefore, birth weight,
portion of underweight women (BMI <18.5 kg/m2) to
However, our study has illustrated the emergent
nearly one-quarter of the survey population.19 Also,
need to identify the etiology of preterm deliveries in
Japan, which is the major fac_tor for the LBW increase.
There are interactio_ ns between the increase in preterm
deliveries and multiple gestations, because multiple
gestations are reported to be at an inc_reased risk for
preterm delivery, compared with singletons.30 They are
our previous study on pregnant women showed that
dietary intake was low, with a mean energy intake of
7827 2080 kJ/day.20 We speculate that the increase
in nutritionally depri¥red underweight women with
insufficient diet while pregnant has led to poor maternal weight gain and is affec_ting optimal fetal growth.
also at an increased risk of LBW even at term, as shown
An increase in both young (<20 y, ears) and
in Table 4. Moreover, women delivering preterm
advanced-aged mothers (>34 years) was observed during the survey period, together with a rise in smoking
infants are at a higher risk of a subsequent pretenTt
deliverY 18
prevalence. Although not statistically significant
(P = 0.06), the OR for LBW in young mothers was 2.26
decrease LBW, further research should be co_ nducted
(95"/. CI = 0.97-5.28) c.ompared with the reference age
to: (i) identify factors influencing preterm deliveries,
group of 20-24 years. We could no_ t demonstrate a
strong effect of smoking and maternal age on LBW
including the use of assisted reproductive technologies; (ii) collect accurate information on smoking and
drinking prevalence in pregnancy; and (iii) monitor
increase, but the present trend, as shown in Figure l
and Table 4, might affect maternal and child health in
the near future. Attention by government officials and
health professionals is needed to_ encourage smoking
In order to develop effective prevention strategies to
weight gain in pregnancy according to maternal
c_essation among young women to prevent LBW
prepregnancy body siz,e to develop appropriate weight
gain goals. A public health approach to educate adolescents to prevent teenage child birth might also be
inf ants.
necessary,
Our present analyses have several limitations due to
the data collection methods used in the CIG survey
First, as already mentioned, participants in this survey
Acknowledgments
were limited to live infants who were able to attend
infant health examinations at local public health cen-
This study was supported by the Kodomo Mirai
Zaidan, Grant for Children's Environment Research
ters. This is most likely to be the reason for the decrease
Project.
in the survey participation rate between 1990 and 2000.
Non-participants in the 2000 survey might have been
mostly LBW, who were either hospitalized, or were
currently ill, although information on non-participants
was not assessed in this survey Our LBW sample
might have been limited to low-risk infants, as shown
in the low percentage of VLBW infants and early pre-
Ref erences
1. Statistics and Information Department, Minister's Secretariat
Ministry of Health Labour and Welfare. Vital Statistics o,f Japan
1980-2000, V0.1. 1. Tokyo: Ministry of Health Labour and
Welfare, 1982-2002. (In Japanese.)
H. Takimoto et al.
2. Ananth CV, Wen SW, Trends in fetal growth among singleton
gestations in the United States and Canada, 1985 through
17. Lang JM, Lieberman E, Cohen A. A comparison of risk factors
for preterm labor and terrn small-for-gestational-age birth.
1998. Sefnin Perinatol 2002; 26: 260-267.
Epide,?tiology 1996; 7: 369-376.
3. Odlind V, Haglund B, Pakkanen M, Olausson PO. Deliveries,
mothers and newborn infants in Sweden, 1973-2000. Acta
Obstet Gynecol Scand 2003; 82: 516-528.
4. Skjaerven R, Gjessing HK. Bakketeig LS. Birthweight by gestational age in Norway. Acta Obstet Gynecol Scand 2000; 79:
440 49,
5. Fujita T, Minowa M, Miura Y, Karniya K. [Risk factors for
neonatal and postneonatal mortality - a record-linkage study
based on vital'statistics.] Nippon Koshu Eisei Zasshi 1994; 41:
34 15. (In Japanese.)
18. Blondel B, Kogan MD. Alexander GR et al. The impact of the
increasing number of multiple births on the rates of preterm
birth. A,11 J Public Health 2002; 92: 1323-1330.
19. Takirnoto H, Yoshiike N, Kaneda F, Yoshita K. Thinness
among young Japanese wornen. Am J Public Health 2004; 94:
1592-1595.
20. Takimoto H, Yoshiike N, Katagiri A, Ishida H, Abe S. Nutritional status of pregnant and lactating women in Japan: A
comparison with non-pregnant/non-lactating controls in the
National Nutrition Survey. J Obstet Gynaecol Res 2003; 29: 96-
6. Alexander GR. Kogan M, Bader D, Carlo W, Allen M, Mor J.
1 03 .
US birth weight/gestational age-･specific neonatal mortality:
1995-1997 rates for whites. Hispanics, and blacks. Pediatrics
2003; 111: e61-e66.
21. Walsh RA, Redman S, Adamson L. The accuracy of self-
7. Barker DJ, Winter PD, Osmond C, Margetts B, Simmonds SJ.
Weight in infancy and death frorn ischaemic heart disease.
22. Secker-Walker RH, Vacek PM, Flym BS, Mead PB. Exhaled
report of smoking status in pregnant 1/¥'omen. Addict Behav
1996; 21: 675-679.
carbon monoxide and urinary cotinine as measures of smoking in pregnancy. Addict
Lancet 1989; 2: 577-580.
8. Eriksson JG, Forsen T. Tuomilehto J, Winter PD, Osmond C,
ehav 1997; 22: 671-684.
23. Chang G, Goetz MA, Wilkins-Haug L. Berman S. Prenatal
Barker DJ. Catch-up growth in childhood and death from
alcohol consumption: Self versus collateral report. J Subst
coronary heart disease: Longitudinal study. BMJ 1999; 318:
427431 .
9. Forsen T, Eriksson JG. Tuomilehto J, Osmond C. Barker DJ.
Abuse Treat 1999; 17: 85-89.
24. Kristensen J, Langhoff-Roos J, Kristensen FB. Implications of
idiopathic preterm delivery for previous and subsequent
Growth in utero and during childhood among women who
develop coronary heart disease: Longitudinal study.
pregnancies. Obstet Gynecol 1995; 86: 800-804,
MJ
25. Siega-Riz AM. Adair LS. Hobel CJ. Maternal underweight
1999; 319: 14031407.
10. Lithell HO, McKeigue PM, Berglund L. Mohsen R, Lithell UB,
Leon DA. Relation of size at birth to non-insulin dependent
diabetes and insulin concentrations in men aged 50-60 years.
BMJ 1996; 312: 406 110.
11. Yoshimura K, Kato K. [A st:udy on the secular trend of average birth weight in the last ten years.] Shoni-Hok'en Kenkyu
status and inadequate rate of weight gain during the third
1994; 53: 557-561. (In Japanese.)
12. Ohmi H, Hirooka K, Hata A, Mochizuki 'Y. Recent trend of
increase in proportion of low birthweight infants in Japan.
trimester of pregnancy increases the risk of preterm delivery.
J Nutr 1996; 126: 146-153.
26. Murphy JF. O'Riordan J, Newcombe RG, Coles EC,
Pearson JF. Relation of haemoglobin levels in first and
second trimesters to outcome of pregnancy. Lancet 1986; 1:
992 995.
27. Martius JA, Steck T. Oehler MK. Wulf KH. Risk factors associated with preterm (<37 + O weeks) and early preterm birth
(<32 + O weeks): univariate and multivariate analysis of 106
Int J Epidenliol 2001; 30: 1269-1271.
345 singleton births from the 1994 st:atewide perinatal survey
of Bavaria. Eur J Obstet Gynecol Repl'od iol 1998 October; 80:
13. Equal Employment. Children and Farnilies Bureau, Ministry
of Health. Labour, and Welfare. [Year 2000 Report of the Chil-
183-189,
dren and Infant Crowtll Survey.] Tokyo: Ministry of Health
28. Rebecca AJ, Kimberly AG, Yvonne WW. Mary SC. Perinatal
Labour and Welfare, 2001 . (In Japanese.)
14. Hanley JA. A heuristic approach to the formulas for popula-
outcomes in singletons following in vitro fertilization: A
tion attributable fraction. J Epiderniol Collrmunity Health 2001;
29, Meis PJ. Goldenberg RL, Mercer BM et al. The preterm prediction study: Risk factors for indicated preterm births.
Maternal-Fetal Medicine Units Network of the National Institute of Child Health and Human Development. Am J Obstet
55: 508-514.
15. Kramer MS. Intrauterine growth and gestational duration
determinants. Pediatrics 1987; 80: 502-511.
16. Abrams B, Newman V. Small-for-gestational-age birth:
Maternal predictors and comparison with risk factors of
meta-analysis, Obstet Gynecol 2004; 103: 551-563.
Gynecol 1998; 178: 562-567.
30. Minakami H, Kosuge S, Fujiwara H. Mori Y. Sato I. Risk of
spontaneous preterm delivery in the same cohort. Am J Obstet
Gynecol 1991; 164: 785-790.
- 204 -
premature birth in multifetal pregnancy. Twin Res 2000; 3: 26,
J. Obstet. Gy/7accol. Res. Vo!. 31, No. 1: 43-49, Febl'uary 2005
Reference birth-length range
in Japan
for
multiple-birth neonates
Noriko Kato and Yuko Uchiyama
Departments of Education Training Technology and Development and Health Promotion and Research National Institute
of Public Health, Saitama, Japan
Abstract
Aim: To clarify the birth length of tvvins according to gestational age.
Metllods: We studied a total of 51 910 Iive-birth-live-birth pairs of twins, 4561 triplet live births and 256 qua-
druplet live births, using data obtained from corresponding birth certificates. The birth length of twins was
analyz,ed according to gestational age.
Results: Compared to singleton neonates, the median birth length of twins was approximately 0.5 cm smaller
after the gestational age of 34 weeks, increasing to approximately 2.0 cm at 42 weeks of gestation. The median
birth length according to gestational age was found to be the greatest in twins, Iower in triplets and the lovvest
in quadruplets, in which the differenc e was <2.0 cm.
Conclusion: The birth length of twins was smaller than that of singletons, but the difference was smaller than
the difference in birthweight between twins and singletons.
Key words: asymmetrical growth, birth length, gestational age, twins.
Background
Since the introduction of assisted reproducti¥'e technology, the rate of multiple births has increased rap-
idly in Japan.1 Required promptly in the clinical
setting, studies on the birthweight of twins have been
conducted in many countries.2 5 Kato has previously
analyzed the birthweight of multiple-birth neonates
according to gestational age, using data from corresponding birth certificates.6
cal.7,8 To determine if fetal growth is symmetrical or
not, other measurements such as birth length and head
circumference should be taken into account.7,8
S ince 1995, the birth-1ength has been inchlded in the
birth certificate, so the authors were able to analyze
birth length according to gestational week for neonates
born in Japan.
Materials and Methods
For the assessment of fetal intrauterine growth, it is
In Japan, birth, death, and stillbirth certificates are cur-
not adequate to use only the birthweight according to
gestational weeks. The intrauterine growth of multiple-birth neonates is often reported to be asymmetri-
base contains information about the neonate, including
rently stored in data files on magnetic tapes. This datathe sex, birthv¥'eight, birth length, gestational age, the
Received: May 6 2004.
Accepted: November 15 2004.
Reprint request to: Dr Noriko Kato, Department of Educ.ation Training Technology and Development. National Institute of Public
Health, 2-3-6 Minami, Wako-shi. Saitama 351-0197 Japan. Email: [email protected]
Supported by a Grant-in-Aid for Scientific Researc.h (KAKENHI. Grant No. 13670407) from The Ministry, of Education, Culture. Sports,
Science and Technology (MEXT) of Japan.
- 205 -
N. Kato and Y, Uchiyama
parity of the mother, and the ages of the father and
mother. Frorn this database, we identified 105 382
twins, 4561 triplets and 256 quadruplets born in Japan
between 1995 and 1999. The data related to multiple
The smoothed standard deviation for each gestational age 'as calculated using linear regression
weighted by the number of cases for each gestational
week.
births were not linked to each other.
The number of subjects at each gestational age is
In order to determine whether both twins of each
shown in Table I .
pair were still alive, the twins were arranged into p.airs,
based on both births occurring in the same rnunicipality, within 10 days of each other, and to parents of the
same age. Using this method, 51 910 Iive-birth-livebirth pairs of twins were selected for analysis in this
study,
Birthweight was recorded to I g, birth length was
rounded to I cm, and gestational age to I day.
The means and standard deviations of gestational
age were calculated for twins, triplets and quadruplets
according to sex and parity, The means and standard
Results
The mean gestational age, birthweight, and birth
length were analyzed according to sex, birth order and
parity, with statistical significance shown in Table 2.
Female, and rnultiparous neonates had a longer gesta-
tional age and the difference was significant among
twins. Male, multiparous and lower birth order neonates were found to ha¥'e a greater birthweight and
deviations of birthweight and birth length were calculated for twins, triplets and quadruplets according to
sex, parity and birth order. The significance of differences between mean values was tested using Student's
10nger birth lengths. These differences were statistically significant, except for the difference between
parity in triplets and between sex in quadruplets.
For multiple-birth neonates, the median birth length
according to gestational age was shown to be the long-
t-test where the comparison was between two groups.
est in twins, followed by triplets and quadruplets
and using one-way ANOVA Where the comparison was
(Figs 1,2). The difference in the median birth length for
between more than three groups.
A reference birth-1ength curve was calculated uSing
Altrnan's method.9 The normality of the distribution
for birth length in each gestational week was tested
each gestational age between singletons and quadruplets was <2.0 cm in both male and female neonates.
Birth length according to the gestational age in
and the null hypothesis was not rejected.
results among Japanese singletons as reported by
twins, as calculated in our study, and according to the
Table 1 Number of subjects used in the analysis for each gestational week
Gestational age
(weeks)
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Twins
Male
154
200
1
1
2
4
9
14
8
3
1
108
22.0
161
180
322
397
448
522
774
219
358
371
485
700
094
660
701
824
859
915
160
781
488
247
24
Quadruplets
Triplets
Female
1
1
2
4
9
14
8
3
1
009
476
710
604
360
925
496
962
643
Male
25
28
45
54
63
74
151
181
240
31
405
336
208
92
12
328
44
･ 206 -
Female
19
27
43
43
46
82
155
164
248
310
405
314
216
130
13
Male Female
2
3
10
8
18
14
2
32
15
35
25
13
11
14
8
1
9
7
9
6
6
3
Birth length of multiple births
Table 2 Gestational age, birthweight and birth length of twins, triplets and quadruplets according to variables
Triplets
Quadruplets
No. of
Standard
T vins
Meandeviation
Mean cases
Standard
deviation
No. of Mean Standard No. of
cases deviation cases
Gestational age (weeks)
Total
102 755
51 965
Male
51 060
Female
57 997
Primipara
44 758
Multipara
36.6
36.6
36.7
36.6
36.7
2.6
2.6
2.5
2.30
2.33
2.26
2.24
2.36
2.33
2.26
o.49
2.6
2.5
l ) ?f'
J ; '
F
4521
2297
2224
3529
984
33,2
4534
2299
2235
3542
984
1 65
33,1
33,2
33.2
33,2
3,0
3,0
2,9
256
2.9
2.9
0.46
o.47
0.45
O.45
0.48
0.46
0.46 J
o.44
l 21
30.1
30.2
30.1
2.4
2.4
2.5
216
39
30
2.5
31.3
l.6
265
1.19
0.35
13 5
l .23
0.38
121
1.15
1.15
0.32
1 .45
1 .24
o.27
0.34
l.23
0.34
1 .22
0.36
0.36
135
Birthweight (kg)
Total
Male
Female
Primipara
Multipara
First born
Second born
Third born
Fourth born
103
51
51
58
44
51
51
Birth length (cm)
Total
100
50
Male
50
Female
56
Primipara
43
Multipara
First born
50
50
Second born
264
974
290
285
979
634
630
621
603
018
673
948
335
286
Third born
Fourth born
p < O 05.
p < O,,O1.
45.3
45.6
45. 1
45.1
45.6
45.4
45.2
o.501
0.47
o.48 J
'
0.49
0.48
0.49
J
3*3 J
3.4
3*3 J
3.5 l
1 .62
1 .64
1 .69
1521
1522
l .65
1 49 1
1.58
1.71
4192
2133
2059
3263
923
3 4
3,5
3*3
1 .68
*
41.2
41.4
40.9
41.2
41.3
41.5
41.2
40.8
1408
1406
1378
J
J
l
4.1
4.1
3.9 J; '
*
216
39
65
65
63
63
240
127
113
4.0
4.1
4.0
4.2 J
4.0 ; '
200
39
61
61
59
59
1.07
37.2
37.5
36.8
36.7
40,0
37.4
37.5
37.6
36.2
J
o.35 ***
J
4.2
4.5
3.8
4.2
2.5 l
4.5
3.8
4.0
4.2
* }P < O.OO1.
Ogawa et al.,10 are shov¥rn in Figures 3 and 4 and in
In triplets, the rnedian birth length was 0,4 cm longer
Table 3. At a gestational age of <36 weeks, the mean
birth length of twins was 0.5 cm shorter than that of
singletons. This difference increased to 2.0cm after
40 weeks of gestation. Male neonates were longer tl Lan
female, and the average difference over all gestational
ages was 0.5 cm.
Twins were classified into four groups according to
birthweight and birth length whether they were larger
in male neonates than in female (Fig. 5; Table 5). In
quadruplets, male neonates were 1.5 cm longer than
female after 34 weeks of gestation (Fig. 6; Table 5).
Discussion
We found that the birth length of twins that were born
after 34 weeks of gestation was longer than that calcu-
ton standard of the corresponding gestational weeklo
lated by Fukuda,u This discrepancy is thought to be
because Fukuda obtained data from a hospital that
(Table 4).
specialized in high-risk pregnancies.
or smaller than the lOth percentile value of the single-
While the rate of twins with birthweights that were
less than the 10th percentile of singletons was 31.6"/o,
that of twins with birth lengths that were less than the
lOth percentile of singletons was 16.00/0. The rate of
twins with birthweights that were less than the 10th
percentile of singletons and also with birth lengths that
The gestational age of multiple-･birth neonates was
shorter than that of singletons, and this difference
increased with an increasing number of fetuses. The
difference in birth length according to sex and parity
was comparable with previous studies.1214
Karn reported that twins exhibited greater weight
were greater than the 10th percentile of singletons was
deficits than singletons after 30 weeks of gestation.14
19.6*/o.
According to a report by Naeye et al,, after 33 weeks of
- 207 -
N. Kato and Y. Uchi yama
55
50
/-*
45
/
1
/
/
/
//
50
45
l'
c'
:_
eh
,:: 40
e)
O,
c
4 bJ)
5
C
(L)
':+J
40
30
,
24 25 26 27 28 29 30 31 32 33 34 35 36
3 5
7 38 39 40 4{ 4'
Gestationai age (weeks)
Figure 3 Birth-lengtl'l percentile curves of twins (male).
(- - -) Singletons, (--) twins. The three lines of each
category correspond to the lOth. 50th and 90th
30
percentiles.
24 26 28 30 32 34 36 38 40 42
55
Figure I Median birth length of multiple-birth neonates
(male). (- -) Singletons, (-) twins, (- - -) triplets. (=)
quadruplets.
50
' // /-'
' Ev 45
:
' / /
t) )f: 40
"J
J::
cc) 35
- /
l. //'
30
50
/
/
/
l
45
/
// "
'
$
::
/
,
eJ)
25
24 25 26 '7 28 29 30 31 32 33 34 35 36 37 38 39 40 41 4_'
Gestational a*'e (weeks)
Figure 4 Birth-1ength percentile curves of twins
(female). (- - -) Singletons, (-) twins. The three lines of
each category correspond to the 10th, 50th and 90th
percentiles.
c::
(L) 40
::
A ;
s
gestation, the mean weight of twins was markedly less
35
than that of singletons.15 Birth･-length curves are said to
l
show few differences, with a significant fall beginning
from 39 weeks of gestation.16 In the present study, the
l
30
/
l
(female). (-- -') Singletons, (-) twins, (- - ) triplets. (=)
birth length showed deficits after 37 weeks of gestation. Cornpared with birthweight, birth length showed
less deficit,8-10 with normal twins said to show 'asymrnetrical' hypotrophy7 The median birthweight curves
of the subjects in this study, which are similar to
quadruplets.
those of McKeown and Record,16 suggest that growth
24 26 28 30 32 34 36 38 40 42
Figure 2 Median birth length of mttltiple-birth neonates
Table 3 Birth-length percentiles of t vins (cm)
Gestational age
(weeks)
1 Oth
27.6
29.0
30.4
31.8
33.2
34.5
35.9
37.3
38.6
39.8
41.0
42.1
43.0
43.9
44.5
45.1
45.6
46.0
24
25
26
?_7
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Female percentile
Male percentile
50th
30.6
32.0
33.4
34.7
36.1
37.4
38.8
40.1
41.4
42.6
43.8
44.8
45.8
46.6
47.2
47.8
48.2
48.6
90th
10th
5 O th
90th
33.6
35.0
36.3
37.7
39.0
40.3
41.7
43.0
26.9
28.3
29.6
30.9
32.3
33.6
35.0
36.4
37.7
39.0
40.2
41.3
42.2
30.1
31.5
32.8
34.1
35.4
33.3
34.6
35.9
37.2
38.5
39.8
44 . 2
45.5
46.6
47.6
48.5
49.3
50.0
50.5
50.9
51.3
36.7
38.1
39.4
41 .2
40.8
42.0
43.2
43 . 8
44 . 3
45 . 2
46.0
46.7
47.2
47.7
48.2
43 . 1
43.7
44.3
44 . 8
45.3
42.5
45.1
46.2
47.3
48.2
49.0
49.6
50.2
50.6
51.0
Table 4 Number of twins above or below the 10th percentile for birthvveight and
birth length
Total ('/.)
Birth length
>lOth percentile ('/.) <10th percentile ('/.)
Birthweight
>10th percentile
<1 Oth perc_entile
Total
4 375 (4.2)
12 279 (11.8)
16 654 (16.0)
66 675 (64.2)
20 591 (19.8)
87 266 (84,0)
71 050 (68.4)
32 870 (31.6)
l03 920 (lO0.0)
50
55
50
45
45
c.
:
eJ)
bJ)
F:; 40
{::
)
a )
J::
40
.::
i
/
35
35
30
27
28 29 30 31 32 33 34 35 36 37 38 39
30
27 28 29 3. O 3132 33 34
Figure 5 Birth-length percentile curves of triplets. (- - -)
Female, (-) male. The three lines of each category correspond to the 10th, 50th and 90th percentiles.
Figure 6 Birth-length percentile curves of quadruplets.
(- - -) Female, (-) male. The three lines of each category correspond to the 10th, 50th and 90th percentiles.
- 209 -
N. Kato and Y. Uchiyama
Table 5 Birth-length percentiles of triplets and quadruplets (cm)
Gestational age
(weeks)
Quadruplets
Triplets
Male percentile
Male percentile
Female percentile
27
28
29
30
31
32
33
34
35
36
37
38
31.7
33.2
34.6
35.9
37.1
38.3
39.4
40.5
41.5
42.5
43.3
44. 1
34.7
36.2
37.6
38.9
40.2
41 .4
42.5
43.6
44.7
45.7
46.6
47.3
37.6
39.2
40 . 7
42,0
43.3
44.5
45 . 7
46.8
47.9
48,9
49 . 8
50.6
31.3
32.6
33.8
35.0
34.1
35.5
36.1
39.1
37.2
38.2
39.2
40.2
41.3
42.3
43.3
40,1
40.9
41.6
42.0
36.7
37.9
44 . 1
44.8
45.3
limitations within the uterus become more marked
with increasing numbers of fetuses.
37.0
38,3
39.6
40.9
42.1
43.3
44.4
45.4
46.4
47.3
48.0
Female percentile
10th 50th 90th 10th 50th 90th
10th 50th 90th 10th 50th 90th
31.2
32.6
34.1
35.7
37.4
3c).O
40.6
33.8
35.2
36.7
38.3
39*9
41.5
43.1
36.3
37.7
39.2
40 . 8
42.5
44,1
45.7
30.9
32.3
33.8
35,1
36.4
37.5
38,4
33.6
35.1
36.5
37.9
39. 1
40.2
41.1
36.4
37.8
39.3
40.6
41.9
43.0
43.9
48 . 5
The present research irLdicates that the same standard
can be used to estimate birth length with gestational
The difference between the median birthweight
age <35 weeks, although the standard for multiple
curve of singletons and that of twins was approxi-
births is necessary after 36 weeks of gestation. This
report shows a birth-1ength reference range for exclusive use in the assessment of multiple births.
In conclusion, the mean birth length of multiple-
mately 0.5 kg at 40 weeks of gestation, which is similar
to the interval between the 10th and 50th percentile
lines of birthweight according to Kat0.6 The interval
between the corresponding median birth-length curve
was approximately 2.0 cm, approximately half of the
interval between the 10th and 50th percentile lines of
birth length. Therefore, the differences were relatively
srnall for birth length.
As for triplets, Yokoyama et al, demonstrated that
birth neonates is shorter than that of singletons. More-
over, the mean birth length of higher order multiple
births is shorter than that of twins, but intrauterine
growth of length was less depressed than growth of
weight. Our results can be used in the assessment of
birth lengths of multiple births in Japan.
the birthweight of triplets was associated with sex, sex
combination and birth order, and that birth length was
associated only with sex.17 The mean birth length that
Acknowledgments
Yokoyama et al, showed indicated a larger value than
this study, which is caused by the difference in study
population.
We thank the personnel of the Department of Statistics
and Information, Ministry of Health, Labor and Wel--
After birth, catch-up growth has been shown to
birth and death certificates. We also thank Ms T Tanaka
and Ms I Morita for technical assistance.
occur in multiple births. Ooki and Asaka showed that
the size deficit at birth was recovered over the first
6 years of life, and no size deficit was observed in
school-age children.18 According to Wilson, body
length is less depressed than weight at birth, and
fare of Japan for copying the magnetic tape data on
Ref erences
1. Imaizumi Y. Recent and long-term trends of multiple birth
rates and influencing factors in Japan. J Epidemiol 1994; 4: 103-
recovery also occurs during the first year of life.19
Buckler and Buckler studied the growth of multiple
birth children at various ages throughout childhood.20
The height of twins was cornparable with the overall
population of singletons, but that of higher multiples
was slightly below average.
Intrauterine growth standards are referred to in the
109.
2. Arbuckle TE, Wilkins R, Sherman GJ. Birth weight percentiles by gestational age in Canada. Obstet Gynecol 1993; 81:
39 8.
3. Buckler JM. Green M. Birth weight and head circumference
standards for England twins. Arch Dis Child 1994; 71: 516521.
4. Glinianaia SV. Skjaerven R, Magnus P. Birthweight percen-
assessment of birth length according to gestational age.
- 2 10 --
tiles by gestational age in multiple births. A population-based
study of Norwegian twins and triplets. Acta Obstet Cynecol
Scand 2000; 79: 450 58.
5
13. Boomama DI. Orlebeke IF, van Baal GC. The Dutch Twin
Register: Growth data on weight and height. ehav Cenet
1992; 22: 247-251.
Min SJ. Luke B. Gillespie B et al. Birth weight references fo. r
twins. Am J Obstet Gynecol 2000; 182: 1250-1257.
6. Kato. N. Reference birthweight range for multiple birth neonates in Japan. BMC Pregnancy Childbirth 2004; 4: 2.
7. Hemequin Y. Rorive S. Vermeylen D. Pardou A. Twins: Interpretation of height-vveight curves at birth Rev Med Brux 1999;
20: 81-85.
8. Winter A. Juez G, Luc_ero E, Donoso E. Intrauterine growth in
full-term twins without risk fac_tors Rev Chil Obstet Cinecol
1994; 59: 123-127.
14. Karn MN. Birth weight and length of gestation of twins,
together with maternal age, parity, and survival rate. Artn
Eugenic 1952; 16: 365-377.
15. Naeye RL. Benirschke K. Hangstrom JWC. Marcus C. Intrauterine growth of twins as estimate from liveborn birth-weight
data. Pediatrics 196. 6; 37: 409 16.
16. McKeown T. Record RG. Observations on foetal growth in
multiple pregnancy in man. J Endocrinol 1952; 8: 386 lO1.
17. Yokoyama Y. Yamashiro M. O_ oki S. Birth weight and height
9. Altman DG. Construction of age-related reference centiles
characteristics of triplets. Nippon Kos hu Eisei Zasshi 2003; 50:
using absolute residuals. Stat Med 1993; 12: 917-924.
10. Ogawa Y, Iwamura T, K,uriya N et al. Birth size standards by
gestational age for Japanese neonates. Jpn J Neonato! 1998; 34:
18. Ooki S. Asaka A. Physical growth of Japanese twins. Acta
624642.
2 1 6-224 .
Genet Med Ge,1lellol (Ro,na) 1993; 42: 275-287.
19. Wilson P¥S. Tvvin growth: initial deficit, reco¥'ery, and trends
in conc_ordance from birth to nine years. Ann Hu,n Biol 1979;
ll. Fuk,uda M. Clinical study of twins. Part 1. Intrauterine
growth curve of twins. Ipn J Neonatol 1990; 26: 366-371,
12. Fenner A. Malm T. Kusserow IJ. Intrauterine growth of
twins. A retrospective analysis. Eur J Pediatr 1980; 133: 119-
6: 205-220.
20. Buckler JM. Buck,1er JB. Growth c_haracteristics in twins and
highter order multiple births. Acta Genet Med Gemellol (Roma)
1987; 36: 197-208.
121.
-211-
Journal of Epidemiology
Young Investigator Award Winner's
Voi, l 4, No, 4 July 2004
Special Article
Strategies for Prevention and Management of Hypertension throughout Life
Katsuyuki Miura
Hypertension has been acknowledged as one of the greatest and established risk factors for cardiovascular diseases. In this special article, strategies for the prevention and management of hypertension
throughout human's life were discussed. Studies showing the relationship of birth weight and height
increase in childhood to future blood pressure suggest that both environments during pregnancy and
during chiidhood and adolescence are important to prevent hypertension. The promotion of a DASH
(Dietary Approach to Stop Hypertension) dietary pattern, rich in fruits and vegetables, is important not
only for treatment of high blood pressure but also for long-term prevention of blood pressure rise as
well. Blood pressure measured in young adulthood can effectively predict long-term risks of cardiovascular and all-cause mortaiity, so population-wide primary prevention of high blood pressure for young
adults is important. Recent large scale cohort studies confirmed that detection and evaluation of hypertension based mainly on systolic blood pressure remains the most practical and easy approach in the
general population for young aduit, middle-aged, and older men and women. Researchers in Asia are
desired to establish high-quality epidemiologic evidences for Asian for the prevention and management
of hypertension.
J Epidemio/ 2004;1 4:1 1 2-1 1 7.
Key words: blood pressure, hypertension, prevention, epidemiology
Introduction
showing results from my related research papers.
Hypertension has been acknowledged as one of the greatest and
established risk factors for cardiovascular diseases (heart diseases
Birth weight
and stroke). Particularly in Asian countries, where the mortality
pressure
and morbidity of stroke are higher than in westem countries, mea-
Recent epidemiologic studies have demonstrated that birth weight
childhood growth, and future bloocl
sures against hypertension are considered very important in the
and other measures of prenatal growth are associated with adult
prevention of stroke.* 3 Hypertension affects a majority of the
blood pressure (BP)5-? and with cardiovascular disease mortality in
elderly, and drug therapies for hypertension have greatly added to
later life.8 ll On the other hand, it has also been suggested in
medical costs in most developed countries. The conquest of
Western populations that short stature is an important risk factor
hypertension is now a major challenge.+
for cardiovascular diseases.12 16 Although Barker et al hypothe-
This special article is written on the occasion that I was given
sized that malnutrition during pregnancy is responsible for the
the Young Investigator's Award of the Japan Epidemiological
development of short stature and overweight as well as of several
Association in January 2004. I have been involved mainly in epi-
risk factors in adult life, including hypertension,i7 socioeconomic
demiologic researches on the prevention and management of
conditions that persist throughout life can cause both lower birth
hypertension, and the award was given for these researches. In
weight and slower increase in height during adolescence. a Some
this article, I would attempt to discuss strategies for the preven-
cross･･sectional within-population studies, especially in children
tion and management of hypertension throughout human's life,
and adolescent,s, have shown a positive relationship between
Received June 23, 2004, and accepted June 29, 2004,
Katsuyuki N/liura. MD. PhD won the Young Investigator Award of the Japan Epidemio!ogical Association in 2003, The surYlmary of
this paper was presented at the 14th Annual Scientific Meeting of the Association in Yamagata. Japan on January 22, 2004,
' Department of Epidemioiogy and Public Health, Kanazawa Medical University, Ishikawa, Japan
Address for correspondence: Katsuyuki Miura, MD, PhD. Department of Epidemiology and Public Health, Kanazawa Medical
University, 1-1 Daigaku. Uchinada, ishikawa, 920-0293, Japan,
-212-
Miura K,
height and BP,19.21 and another inter-population study showed
substantial combined reductions in BP of both nonhypertensive
inverse relation between height and BP. 6 Thus, the underlying
and hypertensive persons. The DASH dietary concept, emphasiz-
mechanism of the association of height with cardiovascular dis-
ing a healthy pattern based on food rather than nutrient intake, has
ease is not yet clear. However, findings on the effect of height
been incorporated into recent dietary guidelines by the American
increase during childhood, independent of birth weight, on cardio-
Heart Association23 and by JNC7 (the Seventh Report of the Joint
vascular disease and its major risk factors are limited.
National Committee on Prevention, Detection, Evaluation, and
To determine whet,her birth weight and childhood growth, espe-
Treatment of High Blood Pressure).29 While the DASH combina-
cially height increase rate, independently relate to BP in adult life,
tion diet is effective in lowering blood pressure, influences of spe-
we conducted a 20-year follow-up study, using the record-linkage
cific foods and food groups (e,g., vegetables, fruits, fish, red
method, in a Japanese population.22 In this study, both birth
meats) on BP have not been well studied long-term. Information
weight and rate of height increase in childhood and adolescence
is especially sparse on relationships of food groups to BP chan_ e
were inversely and independently associated with BP at age 20
in populations followed prospectively for years.
years (Table I ). These results suggest that both environments dur--
We reported relationships of food intake to BP change in a
ing pregnancy and during childhood and adolescence indepen-
prospective cohort study of I ,710 middle-aged men, the Chicago
dently affect subsequent BP Ievel.
Western Electric Study.30 The Generalized Estimating Equation
met,hod was used to analyze relationships of food group intakes to
Food intake and long-term BP increase
average annual BP change, adjusting for age, weight at each year,
By the early 1990's, based on scientific evidence available at the
alcohol, calories, and other foods. Men who consumed 0.5-1.5
time, nutritional guidelines for prevention and control of high
cups vegetables/day were estimated to have 2.8 mmHg less sys-
blood pressure recommended weight control, reduced intake of
tolic BP (SBP) rise in 7 years than men who consumed <0.5
sodium chloride (salt), avoidance of heavy alcohol consurnption,
cups/day. Men who consumed 0.5-1.5 cups fruit/day were esti-
and increased dietary potassium intake.'3"' The DASH (Dietary
mated to have 2.2 rumHg less SBP increase in 7 years than men
Approach to Stop Hypertension) study recently added further
dietary approaches to reduce BP in both nonhypertensive and
who consumed <0.5 cups/day. Beef-veal-lamb intake and poultry
intake were related directly to greater BP rise. These findings lend
hypertensive individuals using a "combination" dietary pattern
further support to the promotion of a DASH-style dietary pattern
during an 8-week intervention.25 2* This dietary pattern emphasizes
not only for treatment of high blood pressure but also for long-
higher than usual intakes of fruit and vegetables and low-fat dairy
term prevention of BP rise as well.
products. It also includes selection of whole grains, poultry, fish,
and nuts, and reduced intake of total fats, saturated fats, choles-
BP in young adults can predict future cardiovascular mortality
terol, red meats, sweets, and sugar-containing beverages. This diet
For middle-aged and older populations worldwide, BP has repeat-
is high in potassium, magnesium, phosphorus, calcium, fiber, and
edly been shown to be a significant risk factor for coronary heart
protein. The DASH-Sodium trial also showed that the combina-
disease (CHD), stroke, and the ma.jor cardiovascular diseases
tion diet plus reduced salt intake (at about 50 mmoUday) yielded
(CVD).*-3 These relationships, for both SBP and diastolic BP
Table 1. Predicted differences in systolic blood pressure (mmHg) at age 20 for I standard deviation higher values of
birth weight, % increase in height, and weight at age 20 estimated by multiple linear regression analysis,
among 2.198 men and 2,428 women born in 1965-1974, Ishikawa, Japan.
Women
Men
1 standard
Predicted
deviation
difference
confidence I standard Predicted confidence
interval deviation difference interval
Model 1
Birth weight
Weight at age 20
0.44 kg
9.4 kg
- I .5
4.4
-2.0
- I .O
,
4.0 4.9
,
0.41 kg
- I .O
- I .4
,
7.3 kg
3 .3
0.41 kg
- I .O
-0.5
3.7
2.9
Model 2
Birth weight
% increase in height (age 3 to 20)
Weight at age 20
0.44 kg
5.4 %
9.4 kg
- I .6
-2. 1
,
-0.7
4.5
Both models are also ad,justed for gestational age.
Modified from reference 22,
- 2 1 3 --
-1.l
-1.1
-O . 2
,
4.0 5.0
4.9 %
7.3 kg
-0.5
- I .4
-O._5
-0.9
3 .4
3_ .O
-O. l
,
3.8
Strategies to OvercorT e Hypertension
(DBP), are continuous, graded, strong, independent of other risk
20 per I ,OOO, translating into estimated shorter lii'e expectancy of
factors, consistent, predictive, and generally assessed as etiologi-
2.2 and 4.1 years. These two strata accounted for 59% of all
cally significant. In contrast, Iong-term observations on blood
excess deaths attributable to SBP/DBP above normal (Figure 1).
pressure and C.HD-CVD mortality in young adults are limited.
These data lend strong support to two strategic concepts: First,
Because major CVD events are rare before age 50 years in men
and 60 in women, studies on risk factors measured at an average
the importance of population-wide primary prevention by safe
nutritional-hygienic means of adverse BP Ievels, so that a sub-
age of about 30 years require long-terrn follow-up or large sample
stantial increase is achieved in the proportion of people in the
sizes to accrue adequat.e numbers of events. The few reports of
population who, throughout life, have favorable levels of BP (and
prospective population-based st.udies are from nested case-control
other risk factors). Second, population-wide efforts for early
investigations in former college students.31'33 Other evidence
detection of children, teenagers, and young adults -- as well as
comes from autopsy studies showing t.hat coronary risk factors
others - with unfavorable BP Ievels, so that therapeutic efforts
relate to early atherosclerotic lesions in young adults.34 36 Although
can be instituted early, first and foremost to improve lifestyles.
hypertension treatment guidelines are usually considered applicable for persons ages 1 8 and older,23,24,29 there is limited documenta-
Importance of SBP and DBP im various age groups
tion supporting screening and treatment of young adults.
Some recent epidemiologic studies reported that pulse pressure
'I'he Chicago Heart Association Detection Project in Industry
(pp), the difference between SBP and DBP, is a useful predictor
Study is one of the largest and longest prospect,ive studies provid-
for CHD or total CVD especially in middle-aged or older peo-
ing CVD rnortality data. Approximately 1 1,000 men ages 18-39
ple.38 41 These reports emphasized the importance of PP as a CHD
at baseline (30 years on average) were followed for 25 years, and
or CVD risk factor, especially because PP is often higher after age
we reported the relationship of baseline BP to 25-year CHD,
50, apparently due to increased arterial stiffness.42, 43 In regard to
CVD, and all-cause mortality.37 The main findings on this cohort
prior reports on PP, many did not compare the significance of PP
of young adult men are: ( 1) BP measured in young adulthood pre-
with that of SBP or DBP, and sorne others were studies on hyper-
dicted long-term risks of CHD, CVD, and all-cause mortality. As
tensive persons only. Therefore, it was uncertain whether PP is
in middle-aged and older persons,1 3 relationships of SBP, DBP,
superior to SBP or DBP in predict=ing future CHD, CVD, and all-
and SBP/DBP (JNC-VI strata23) to mortality were generally grad-
cause deaths in various age-sex groups of the general (i.e., appar-
ed, strong, and independent. (2) Multivariate-adjusted HRS tended
ent.ly healthy) population. Moreover, because recent discussions
to be greater for SBP than DBP, and similar in size to those for
have emphasized the importance of SBP compared to DBP,+4-+6
middle-aged men. And (3) for the two large strata with high-nor-
and these are strongly correlated, it is also important to assess
mal BP and with stage I hypertension, 25-year absolute risks and
whet.her DBP has any additional role in predicting risks indepen-
absolute excess risks of mortality were substantial, e.g., all causes
dently from SBP,
death rates of 63 and 72 per I ,OOO, absolute excess rates of 10 and
We reported relat.ions of four BP indices PP, SBP, DBP, and
50
1 20
43.8
(,D
CSHo 100
h
If)
c¥
Fl
107.
C EI % of all excess deaths
40 v::
-Excess all-cause mortality
80
es
(L)
.-
o
o 60
o^
.H
o
t'D
(,D
(L)
o
24.6
o
51.4
15.6
40
20
30 eo(,oQ)
20 c:$
9.7
6.2
' 0.0
O ptimal
10
o
; Q
19.7
1 1 9 (reference)
O
qH
10.1
O
Normal High-normal
Hypertension, Hypertension, Hypertension,
stage 1
stage 2
stage 3
Figure 1. Absolute excess risk per I ,OOO in 25 years and percentage of all excess deaths frorn all causes in strata of JNC-VI
classification23 in l0,874 men aged 18-39 years at baseline, the Chicago Heart Association Detection Project in Industry,
Percentage of all excess deaths was calculated from estimated number of excess deaths compared with the normal blood
pressure stratum by JNC-VI criteria during 25 years of follow-up. Modified from reference 37.
-214-
Miura K,
rnean arterial pressure (MAP) - to 25-year mortality risks from
sion and cardiovascular diseases thro. ughout life.
CHD, CVD, and all causes in five population cohorts (total
28,360 men and women) classified by age and sex from the
Acknowledgement
Chicago Heart Association Detection Project in Industry Study.+'
The author expresses appreciation to Drs. Hideaki Nakagawa,
The main findings from this study were: (1) Relationships of PP
Jeremiah Stamler, and Philip Greenland, whose great contribution
were less strong than those of SBP for all endpoints in all age-sex
made this work possible. The aut,hor also acknowledges the Japan
groups studied. (2) Relationships of PP were less strong than
Epidemiological Association and the Editorial Board of the
those of DBP for all endpoints in middle･-aged men and women
Journal of Epidemiology for giving an opportunity to write this
and in older women. (3) Among the four BP indices, the strongest
special article.
relationship was observed either for SBP or MAP in all age-sex
groups. (4) Relationships of SBP to mortality tended to be
stronger than or similar to those of DBP. And (5) with control for
Ref erences
1 . Stamler J, Stamler R, Neaton JD. Blood pressure, systolic and
diastolic, and cardiovascular risks: US population data. Arch
SBP, DBP was positively and significantly related to mortality in
Intem Med 1993; 153: 598-615.
middle,-age men and women, but not in younger men and older
2. MacMahon S, Peto R. Cutler J, Collins R, Sorlie P, Neaton J,
men and women.
et al. Blood pressure, stroke, and coronary heart disease: part
As to implications of these results for public health policy and
clinical practice: (1) They affirm continued emphasis on SBP,++-+"
l , prolonged differences in blood pressure: prospective obser-
particularly for younger men and older people. For middle-aged
vation studies corrected for the regression dilution bias.
L,ancet 1990; 335: 765-74.
people ages 40-59, DBP should be given concomitant careful consideration because of its strong independent relationship to mor-
3. Eastern Stroke and Coronary Heart Disease Collaborative
tality. (2) In younger and middle-aged people, emphasis on PP
Research Group. Blood pressure, cholesterol, and strok.e in
eastern Asia. L,ancet 1998; _352: 1801-7.
should be avoided. There is no evidence, in a general population
less than age 60, showing that PP is superior to. SBP in predicting
4. Miura K, Daviglus ML, Greenland P, Stamler J. Making pre-
CVD or total mortality. Emphasizing risks associated with PP is
vention and management of hypertension work. J Hum
Hypertens 2001 ; 1 5 : I -3.
likely to underestimate true risks. And (3_ ) relationships of MAP
to risk were generally as strong as or slightly stronger than those
5. Law CM, Shiell AW. Is blood pressure inversely related to
of SBP. However, use of this index may not be practical in daily
birth w'eight? The strength of evidence from a systemic
review of the literature. J Hypertens 1 996; 14:935-41 .
clinical and pub. Iic health practice, because there are no guidelines
for hypertension diagnosis and management using MAP.
6. L,aw CM, de Swiet M, Osmond C, Fayers PM, Barker DJ,
Detection and evaluation of hypertension based mainly on SBP
Cruddas AM, et al. Initiation of hypertension in utero and its
amplification throughout life. BMJ 1993. ;306:24-7.
remains the most practical and easy approach in the general popu-
lation for young adult, middle-aged, and older men and women
7. Curhan GC, Willet WC, Rimm EB, Spiegelman D, Ascherio
(at least up to about age 63 years). After this report, several cohort
AL,, Stampfer MJ. Birth weight and adult hypertension, dia-
studies including older people did the same kind of analysis and
betes mellitus, and obesity in US men. Circulation
1996;94:3246-50.
showed that the relationship of PP to mortality from total cardio-
vascular diseases and coronary heart disease was less strong than
8. Barker DJP, Winter PD, Osmond C, Margetts B, Simmonds
SJ. Weight in infancy and death from ischaemic heart dis-
those of other BP indexes.*8 50
ease. Lancet 1989;ii:577-80.
9. Martyn CN, Barker DJP. Osmond C. Mothers' pelvic size,
Making evidences for Asian people
fetal growth, and death from stroke and coronary heart dis-
Very fortunately, I was able to contribute to long-term, Iarge-
ease in men in the UK. Lancet 1996;348: 12648.
scale cohort studies in Chicago. However, most study participants
in these studies were Caucasian, and, as it is comrnonly true for
many other major hypotheses in preventive cardiology, epidemio-
10. Frankel S, Elwood P, Sweetnam P, Yarnell J, Smith GD.
Birthweight, body-mass index in middle age, and incident
coronary heart disease. Lancet 1996;348: 1478-80.
logic evidences for Asian people tend to be sparse. Recently I
good opPortunity to participate in the INTERnational
11. Rich-Edwards JW, Stampfer MJ, Manson JE, Rosner B,
cooperative study of MAcro- and micro-nutrients and blood
Hankinson SE, Colditz GA, et al. Birth weight and risk of
Pressure (the INTERMAP) and found that there are big differ-
cardiovascular disease in a cohort of women followed up
ences in body mass, fat intake, cigarette smoking, etc., between
since 1976. BMJ 1997;315:396-400.
12. Miura K, Nakagawa H, Greenland P. Height-cardiovascular
have had
Asian and Western people.'*'5' Strategies for the prevention and
management of hypertension and cardiovascular diseases for
Asian would be different from those for Western people,
disease relation: where to go from here? Am J Epidemiol
Researchers in Asia should establish high-quality epidemiologic
2002;155:688-9.
13. Marmot MCJ, Rose CJ, Shipley M, Hamilton PJ. Employment
evidences for Asian and accomplish the prevention of hyperten-
grade and coronary heart disease in British civil servants. J
-215
Strategies to Overcome Hypertension
Epiderniol Comm Health 1978;32:244-9.
Intern Med 1999; 159:285-93.
14. Rich-Edwards JW, Manson JE, Stampfer MJ, Colditz GA,
Willett WC, Rosner B, et al. Height and the risk of cardiovas-
28. Krauss RM, Eckel RH, Howard B, Appel LJ, Daniels SR,
Deckelbaum RJ, et al. AHA Dietary Guidelines: revision
2000: A statement for healthcare professionals frorn the
cular disease in women. Am J Epidemiol 1995; 142:909- 17.
Nutrition Cornmittee of the American Heart Association.
15. Njolstad I, Arnesen E, Lund-Larsen PG. Body height, cardiovascular risk factors, and risk of stroke in middle-aged men
and women: A 14-year follow-up of the Finnmark study.
Circulation 1996;94:2877-82.
Circulation 2000; 102:2284-99.
29. Chobanian AV, Bakris GL, Black HR, Cushman WC. Green
LA, Izzo JL Jr, et al. The Seventh Report of the Joint
16. Whincup PH, Cook DG, Adshead F. Taylor S, Papacosta O,
National Committee on Prevention. Detection, Evaluation,
Walker M, et al. Cardiovascular risk factors in British chil-
and Treatment of High Blood Pressure: the JNC 7 report.
JAMA 2003;289: 2560-72.
30. Miura K, Greenland P, Starnler J, Liu K, Daviglus ML,
dren from towns with widely differing adult cardiovascular
mortality. BMJ 1996;3 1 3:79-84.
17. Barker DJP, Gluckman PD, Godfrey KM, Harding JE,
Nakagawa H. Relation of vegetable, fruit, and meat intake to
Owens JA, Robinson JS. Fetal nutrition and cardiovascular
7year blood pressure change in middle-aged men: the
disease in adult life. Lancet 1993;341 :938-41.
Chicago Western Electric Study. Am J Epidemiol
1 8. Crouse JR 3rd. Reduced height for weight and cardiovascular
2004;159:572･ 80.
3 1 . Paffenbarger RS Jr, Notkin J, Krueger DE, Wolf PA, Thome
disease. Lancet 1993;341 :93 1-2.
19. Rosner B, Prineas RJ, Loggie JM, Daniels SR. Blood pres･-
MC, LeBauer EJ, et al. Chronic disease in former college stu･-
sure nomograms for children and adolescents, by height, sex,
dents. II. Methods of study and observat.ions on mort.ality
and age, in the United St.ates. J Pediatr 1993; 123:871-86.
from coronary heart disease. Am J Public Health 1966; 56:
20. Hashimoto N, Kawasaki T, Kikuchi T, Uchiyama M. Criteria
of normal blood pressure and hypertension in Japanese
962-7 1 .
32. Paf'fenbarger RS Jr, Wing AL. Characteristics in youth pre･
preschool children. J Hurn Hypertens 1997; 1 1 :35 1-4.
disposing to fatal stroke in later years. Lancet 1967; 1: 753-4.
21. Rona RJ, Qureshi S, Chinn S. Factors relat.ed to total choles-
33. Paffenbarger RS Jr, Wing AL. Chronic disease in former col-
terol and blood pressure in British 9 year olds. J Epidemiol
lege students. X. The effects of single and multiple character-
Community Health 1996;50:5 12-8.
istics on risk of fatal coronary heart disease. Am J Epidemiol
22. Miura K, Nakab'awa H, Tabata M, Morikawa Y, Nishijo M,
Kagarmmori S. Birth weight, childhood growth, and cardio-
34. Berenson GS, Srinivasan SR, Bao W, Newman 111 WP, Tracy
vascular disease risk factors in Japanese aged 20 years. Am J
RE, Wattigney WA, for the Bogalusa Heart St,udy.
Epidemiol 200 1 ; 1 53 :783-9.
Association bet.ween multiple cardiovascular risk factors and
1969; 90: 527-35.
23. The Joint National Committee of Prevention, Detection,
atherosclerosis in children and young adults. N Engl J Med
Evaluation, and Treatment of High Blood Pressure. The sixth
report of The Joint National Committee of Prevention,
Detection, Evaluation, and Treat,ment of High Blood
1998; 338: 1650-6.
35. Newman 111 WP, Freedman DS, Voors AW, Gard PD,
Srinivasan SR, Cresanta JL, et al. Relation of serum lipopro-
Pressure. Arch Int.em Med 1997; 157:241 3-46.
tein levels and syst.olic blood pressure to early atherosclero-
24. The Guidelines Subcomrnittee of the World Health
sis: the Bogalusa Heart Study. N Engl J Med 1986; 314: 138-
Organization - International Society of Hypertension (WHO-
ISH) Mild Hypertension Liaison Committee. 1999 World
44.
36. McGill HC Jr, McMahan CA, T'racy RE, Oalmann MC,
Health Organization - International Society of Hypertension
Cornhill JF, Herderick EE, et al. Relation of a postmortem
Guidelines for the Management. of Hypertension. J Hypertens
renal index of hypertension to atherosclerosis and coronary
1999;17:151-83.
artery size in young rnen and women: Pathological
25. Appel LJ, Moore TJ, Obarzanek E, Vollmer WM, Svetkey
Determinants of Atherosclerosis in Youth (PDAY) Research
LP, Sacks FM, et al. A clinical trial of the effects of dietary
Group. Arterioscler Thromb Vasc Biol 1998; 18: I 108-18.
patterns on blood pressure. N Engl J Med 1997;3_ 36: 1 1 17-24.
37. Miura K, Daviglus ML, Dyer AR, Liu K, Garside DB,
26. Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA,
Stamler J, et al. Relationship of blood pressure to 25-year
Harsha D, et al. Effects on blood pressure of reduced dietary
mortality due to coronary heart disease, cardiovascular dis-
sodium and the Dietary Approaches to St,op Hypertension
eases, and all causes in young adult men: the Chicago Heart
(DASH) diet. DASH-Sodium Collaborative Research Group.
Association Detection Project in Industry. Arch Intem Med
N Engl J Med 2001 ;344:3- 10.
2001;161:1501-8.
27. Svetkey LP, Simons-Morton D, Vollmer WM, Appel LJ,
38. Franklin SS, Khan SA, Wong ND. Larson MG, Levy D. Is
Conlin PR, Ryan DH, et al. Effects of dietary patterns on
pulse pressure useful in predicting risk for coronary heart dis-
blood pressure: subgroup analysis of the Dietary Approaches
ease? The Framingham Heart Study. Circulation 1999; 100:
to Stop Hypertension (DASH) randomized clinical trial. Arch
354-60.
- 21 6 -
M'ura K,
39. Benetos A, Rudnichi A, Safar M, Guize L. Pulse pressure and
indexes in the prediction of 25-year cardiovascular and all-
cardiovascular rnortality in normotensive and hypertensive
cause mortality rates: The Chicago Heart Association
subjects. Hypertension 1998;32:560-4.
Detection Project in Industry Study. Hypertension
40. Benetos A, Safar M, Rudnichi A, Smulyan H, Richard JL,
Ducimetieere P, et al. Pulse pressure: a predictor of long-
2001;38:232-7.
48. Domanski M, Mitchell G. Pfeffer M. Neaton JD, Norman J,
term cardiovascular mortality in a French male population
Svendsen K, et al. Pulse pressure and cardiovascular disease-
Hypertension 1997; 30: 1410-5.
related mortality: follow-up study of the Multiple Risk Factor
Intervention Trial (MRFIT). JAMA 2002;287:2677-83.
41. Madhavan S, Ooi WL., Cohen H, Alderman MH. Relation of
pulse pressure and blood pressure reduction to the incidence
49. Prospective Studies Collaboration. Age-specific relevance of
of myocardial infarction. Hypertension 1994;23:395-401 .
usual blood pressure to vascular mortality: a meta ･analysis of
42. Franklin SS, Gustin IV W, Wong ND, Larson MG, Weber
individual data for one million adults in 61 prospective studies. Lancet 2002;360: 1903- 13 .
MA, Kannel WB, et al. Hemodynamic patterns of age･･related
changes in blood pressure: The Framingham Heart Study.
50. Asia Pacific Cohort Studies Collaboration. Blood pressure
indices and cardiovascular disease in the Asia Pacific region:
Circulation 1997;96:308l5.
a pooled analysis. Hypertension 2003;42:69-75.
43. Safer ME. Pulse pressure in essential hypertension: clinical
5 1 . Stamler J, Elliott P, Dennis B, Dyer AR, Kesteloot H. L,iu K,,
and therapeutical implications. J Hypertens 1 989;7:769-776.
et al. INTERMAP: background, aims, design, methods, and
44. Black HR. The paradigm has shifted, to systolic blood pres-
descriptive statistics (nondietary). J Hum Hypertens
sure. Hypertension 1 999;3. 4:386-7.
45. Lloyd-Jones DM, Evans JC, Larson MG, O'Donnell CJ, L,evy
D. Differential impact of systolic and diastolic blood pressure
2003 ; 1 7 : 59 1 -608 .
52. Z,hou BF, Stamler J, Dennis B, Moag-Stahlberg A, Okuda N,
Robertson C, et al. Nutrient intakes of middle-aged men and
level on JNC-VI staging. Hypertension 1999;34:38 1-5.
46. Kannel WB. Elevated systolic blood pressure as a cardiovas-
women in China, Japan, United Kingdom, and United States
in the late 1990s: the INTERMAP study. J Hum Hypertens
cular risk factor. Am J Cardiol 2000;85:25 1 -255.
47. Miura K, Dyer AR, Greenland P, Daviglus ML, Hill M, Liu
K, et al. Pulse pressure compared with other blood pressure
-217-
2003 ; 1 7 : 623-30.
日産婦誌57巻10号
学際領域の診療
lnterdisciplinary Practice
妊産婦と栄養
Nutrition during Pregnancy
はじめに
近年のわが国における生活習慣の変化に伴い，肥満症の頻度は激増しており，肥満に起
因する種々の疾患や合併症の罹患率が増加している，体格指数（Bodymasslndex：
BMl）は，個人の栄養状態をみる簡易な指標である．肥満学会では，女性の場合，BMIが
22において疾患罹患度の最も低い指数であると設定し、これに基づき，標準体重（身長
（m）×身長（m）×22）を算出するよ
うに提唱している1）．興味深いこと
に，50年前のわが国では，いずれ
の年代層もB酬は健康的と考えら
れる22前後でほぼ一定であるのに
対し，時代の推移とともに年代間の
B蝋の解離が認められる（図1）．
一方，最近肥満の頻度が高くなって
いることは周知の事実であるが，女
性に限ってみると、年代によって肥
満の頻度が異なっτいることに留意
すべきである，すなわち図2に示
25
竃24
50歳台
40歳台
窃23
と22
濫21
ユ
“ 一一
30歳台
26∼29歳
195019601970198019901995（年）
日本人女性の年代別BMlの推移（厚生労働
（図璽）
すように，肥満（BMI：25以上）頻
省）
度の経時的推移として30∼50歳代
まではむしろ減少しており，その後
増加していることがわかる，さらに
やせの頻度をみると，40歳代まで
増加していることがわかる（図3）。
これらの現象はわが国の女性におい
ても白人と同様、若いときにやせて
いるにもかかわらず，その後，aging
とともに脂肪蓄積が増加することを
示すデータであり，これは近年の女
性における生活習慣病の原因を示す
重要な現象である．また産婦人科領
域では，肥満ややせの妊婦がハイリ
スク妊娠であることや，肥満が多嚢
胞性卵巣症候群や子宮体癌と関連す
ることが知られており，産婦人科医
厘昭和57年騒平成4年騒職14年
（％）
35
30
25
20
15
10
5
0
31，533．3
3122a33α・25愚8
2582a5 256籔4．1
翻9，0
14．914，1
11．O
926，17，0
20∼ 30∼ 40∼
29歳 39歳 49歳
（図2）
わが国の年代別肥満女性の推移（厚生労働
省）
（肥満 BMl：25以上）
一218一
2005年10月
は生活習慣病の予防を十分に意識
し，日常診療にあたるべきである．
（％）
30
回亟．騨成竺團平成購
本稿では女性，特に妊産婦の栄養
を中心に，エネルギー量の設定方法
と，各種栄養素の摂取について概説
25。226つ
する．
15・
妊産婦の食事摂取基準
食事摂取墓準とは健康を保持し，
25
20
15，1
11，4
10
5
0
20∼
9，9
a魔 567ρ58ao70a2
13。312．4
9．9
3．5， 3．2 4．1
30∼ 40∼ 50∼ 60∼
70歳
毎日の生活を健全に営めるようにす
29歳 39歳 49歳 59歳 69歳以上
るためには，どのような栄養素をど
のくらいとればよいかというエネル
（図3）
わが国の年代別やせ女性の推移（厚生労働
ギーおよび各栄養素の摂取量の墓準
省〉
を示したものである，以前はエネル
ギーや栄養素の欠乏の予防という点
が重視されていたが，最近では生活習慣病の予防や過剰摂取による健康障害の予防も目的
としている点に留意すべきである．このような背景下，厚生労働省は日本人の食事摂取墓
準を5年ことに策定し改訂してきた，平成17年度から21年度まで間に使用される食事摂
取墓準は「日本人の食事摂取基準（2005年版）j2）によるものである．
妊産婦の栄養管理を考えるうえで特に留意すべき点は，第1に妊娠・分娩・産褥に伴っ
て母体代謝が大きく変化すること，第2に児の正常な発育を促すために必要にして十分
な栄養を供給しなければならないことである，しかしながら，ヒトの妊娠時の栄養に関し
て以上のような点を満たす研究を構築することは難しく，現実には実態調査と理論値に墓
づいて摂取エネルギー量や必要栄養素量が決定される．
妊婦の場合，該当する年齢の非妊娠女性の食事摂取基準値に対応して算定すればよい，
1．エネルギー
エネルギーは栄養素とは異なる概念を用いて策定されている，すなわち，成人の場合，
エネルギーは体重を維持するために，ある一定量のエネルギー摂取が必要であり，これと
エネルギー消費量が釣り合って体重に変化のない状態が最：も望ましいエネルギー摂取状態
であると考えられる，妊婦や授乳婦については，一般（非妊娠時）の女性のエネルギー所要
量に妊娠・授乳に伴っτ必要となるエネルギー量を付加して必要量が定められている．一
般に妊娠・授乳期女性では身体活動レベルは多少制限されると考えられる．したがって，
この時期の身体活動レベルは表1に示すように，「工（低い）」，あるいは肛（ふつう）」に
属するものとして計算される．妊娠の継続期間については個人差があり，胎児発南にも個
体差があり，授乳の期間や泌乳量についても個人差が大きいという問題点があるが，これ
らにより必要量に差を設けることは困難であるので，それぞれを平均的なものと仮定して
必要量が算定される，また近年勤労女性の割合も高くなってきており，個々の症例におけ
る身体活動レベルの設定には注慧を要する，
次に妊娠可能年齢女性の墓礎代謝量は表2に示すとおりである．推定工ネルギー必要
量は原則として，基礎代謝量×身体活動レベルで計算されるので，表3の一番右側のカ
ラムに示すとおり，身体活動レベルが「低いj，「ふつうjで推定エネルギー必要量が求め
られる，ところで身体活動レベルとは，1日のエネルギー消費量を1日当たりの基礎代
謝量で除した指数である．エネルギー消費量を最も正確に測定する方法が二重標識水法で
あり，本法に基づくデータにより，身体活動レベルは表1のように，「低い」，「ふつう！，「高
一219一
（表1）身体活動レベル別にみた活動内容と活動時間の代表例（15∼69歳1））
身体活動レベル＊
8常生活の内容
低い（1）
生活の大部分が座位
で，静的な活動が中
心の場合
8
睡眠（1．0）
座位または立位の
高い（皿）
ふつう（n）
1．75 （1，60∼1．90）
1．50 （1．40∼1．60）
座位中心の仕事だが，職
場内での移動や立位での
作業・接客等，あるいは
通勤・買物・家事・軽い
スポーツ等のいずれかを
含む場合
2．00 （1．90∼2。20）
移動や立位の多い仕事へ
の従事者．あるいは，ス
ポーツなど余暇における
活発な運動習慣をもって
いる場合
7∼8
7
13∼14
11∼12
10
1∼2
3
3∼4
1
2
3
O
O
O∼1
静的な活動（1．5）
ゆっくりした歩行
や家事など低強度
の活動（2．5）
長時悶持続可能な
運動・労働など中
等度の活動（普通
歩行を含む）（4．5）
頻繁に休みが必要
な運動・労働など
の高強度の活動
（7．0）
＊代表値
個々の活動のレベルの数値の単位は時闘／臼
（表2）妊娠可能年齢女性の墓礎代謝量1）
年齢（歳）
基礎代謝量基準値
（kcal／kg体重／日）
18∼29
30∼49
基準体重（kg）
23．6
21．7
50．0
52．7
基礎代謝量＊
（kcal／日）
1，180
1，140
＊基礎代謝量＝基礎代謝基準値（kc∂1／kg体重／E〕）×基準体重（kg）
（表3）妊娠可能年齢女性の推定工ネルギー必要量1）
年齢（歳）
基礎代謝量基準値
（kc∂1／kg体重／日）
基準体重（kg）
基礎代謝量＊
（kc∂レ日）
15∼17
25．3
50．0
1，270
18∼29
23．6
50．O
1，180
30∼49
21．7
52．7
1，140
＊基礎代謝量＝基礎代謝量基準値（kcal／kg体重／日）×基準体重（kg）
＊＊推定エネルギー必要量謂基礎代謝量x身体活動レベル＊＊＊
＊＊＊身体活動レベル；1：1．50 H：1．75
−220一
推定エネルギー
必要量＊＊（kc∂i／8）
1：1，905
H：2，222
1：1，770
H：2，065
1：1，710
H：1，995
2005年10月
（表4）妊婦・授乳婦の推定必要工ネルギー量1）
生活活動
生活活動強度n
（軽し
（中等度）
1．77
2，065
櫓∼29歳
1．7
1，995
30∼49歳
妊婦
十50 十25（
十50 十250 十500＊
十500＊
十4
授乳婦
十450
＊それぞれ妊娠初期・中期・末期の付加量を示す（単位二kc∂1）
い1の3つのカテゴリーに区分された，
たとえば女性の年齢が18∼29歳であれば非妊娠時の墓礎代謝量は1，180kcal／Elであ
る（表2）．したがって身体活動レベルが1の場合，非妊娠時の推定工ネルギー必要量は
1，180kcal／日×1．5＝1，770kcal／日となる（表3），また身体活動レベルが「ふつうjの
場合，1，180kcal／日×1．75＝2，065kcal／1ヨとなる，同様に30∼49歳なら1，710（身体
活動レベル：工）∼1，995（身体活動レベル：皿）kca！と算出される（表3）．妊娠中および
産褥期のエネルギー付加は，表4のとおりである．したがって妊娠時の必要工ネルギー
量は，妊娠初期には＋50kcal，妊娠中期では＋250kcal，妊娠末期では＋500kcaiの付
加量がそれぞれ加えられ，最終的な推定エネルギー必要量が求められる．授乳期では＋450
kcalとされている（表4）。
さて，エネルギー付加量の算定の根拠は以下のとおりである，まず妊娠時の墓礎代謝量
の増加およびHytten∂ndしeitch，3）の妊娠期間の酸素消費量の研究などから算定された
妊娠全期間の墓本エネルギー増加量は約27、000kcalで，それに蓄積蛋白質量900gすな
わち約5，000kcal，蓄積脂肪量4kgすなわち約36，000kcal，計68，000kcalの付加が
必要と考えられ，さらに消化吸収効率を考慮に入れ，約70，000kc∂i強のエネルギー量の
付加が必要と考えられる，妊婦における推定工ネルギー必要量に関して，2004年にFAO4）
は，妊娠期別に付加量を示している，すなわち，縦断的研究によると，妊娠中は身体活動
レベルが初期と末期において減少する一方，墓礎代謝量は末期に大きく増加する，その結
果，総エネルギー消費量の増加率は妊娠初期・中期・末期それぞれ，1％，6％，17％と
なる．これらの値は妊娠中の母体の体重増加率とほぼ一致しており，消費量の変化分は＋
20kcai／日，＋85kc∂1／E3，＋310kcal／日となる，一方，妊娠時期別のたんぱく質の蓄
積量と体脂肪の蓄積量を考慮に入れてまとめて50kcal単位で丸めると，妊娠初期・中
期・末期ではそれぞれ＋50kcal／日，＋250kcal／日，＋500kcal／日となる，
したがって妊娠全期間のエネルギー付加量は、妊娠前半期50kcal／〔ヨ×98日翼4，900
（kcal）と妊娠中期250kcal／日×84日＝21，000（kcal），後半期500kcal／El×848＝
42，000（kcal）で，合計67，900kcalとなり，先述のHytten andしeitchの妊娠時のエ
ネルギー付加量の理論値にほぼ合致するものといえる，
ただし，妊娠前半期と妊娠後半期の付加量の比率は，時代の変遷と各国によって考え方
が異なる，たとえば1985年には上記WHO（FAO／WHO／UNU）のテクニカルレポート5）
では，妊娠全期間を通じてエネルギー付加量を一定にしている，これは妊娠初期・中期に
脂肪細胞にエネルギーが蓄積され，これが妊娠末期に胎児の発育に消費されるのであれば，
妊娠後半期にエネルギー量を付加する必要はないという考え方による．現在の英国でも同
様の考え方で妊娠時には一律200kc∂1の付加量を定めている，
一方，授乳期のエネルギー必要量は，総工ネルギー必要量と泌乳量相当分の和から体重
減少分を減じたものである．総工ネルギー必要量は非妊娠時と同様と考えられる，また日
一221一
本人の母乳の平均分泌量は780mzとして計算されている．母乳1z当たりの母乳分泌によ
るエネルギー損失は661kcaz／zであり、泌乳量相当分＝0．78（z）×661kcaz／z÷0．8（エ
ネルギー変換率）＝644kcaz／日となる，また体重減少分については，減少分のエネルギー
を6，500kcaz／kg体重，体重減少量を0．8kg／月とすると，6，500kcaz／kg体重×0．8kg／
目÷30E〕譜173kcaz／Elとなる，以上を考慮に入れると授乳期の1El平均付加工ネルギー
は644−173瓢471kcazとなり，値を丸めて450kcazと算定される．母乳を与えない場
合のエネルギー付加は当然のことながら必要ない，
2．栄養素
（1）たんぱく質
たんぱく質は生命の維持に最も基本的な物質である．体たんぱく質蓄積量は体力リウム
増加量より間接的に算定できる．Hytten andしeitchの報告3〉により妊娠末期のたんぱく
質量は中期の2倍であること，初期はたんぱく質の蓄積量が無視しうることより，妊娠
時の付加量の推奨量を10gとして策定されている，妊娠時期別の付加量設定はなされて
いない．
一方，たんぱく質摂取目標量は、種々の報告より2．Og×体重／日以上の摂取で高窒素血
症となることから，この値未満にとどめることを適当と考えられている．一方、たんぱく
質の食事摂取基準は総エネルギー摂取量に占める割合，すなわちエネルギー比率（％エネ
ルギー）で示す．たんぱく質のエネルギー比率は20％未満とされている．
（2）脂質
脂質はエネルギー産生の主要な墨質である．脂質にはたんぱく質や炭水化物から生合成
されるものがある．米国，カナダの報告によると，脂肪工ネルギー比率は20％以上がよ
いとされている，ただし脂肪工ネルギー比率が高いとメタボリックシンドロームの増加す
ることが明らかとなっている．わが国における脂肪工ネルギー比率に関するデータはなく，
国民栄養調査より25％とされている，一方，妊娠時には非妊娠時と同様，20∼30％の脂
肪工ネルギー比率の目安量として設定されている．妊娠時期には生理的に初期から中期に
かけて脂肪が蓄積され脂肪同化の方向へ進み，末期には異化方進となるので，妊娠期間別
の設定を変えなくてもよいものと考えられる，
また脂肪はエネルギー源としての概念のみならず，栄養素としてとらえる必要もある．
特にアラキドン酸やDHAは神経組織の重要な構成脂質である．したがって妊娠時には胎
児神経組織の器富形成のためにもより多くのn−3系脂肪酸の摂取が必要となる，なぜなら
DHAは胎盤を介しτ胎児に移行するからである．魚由来n−3系脂肪酸摂取不足と早産あ
るいは低出生体重児の相関を示す報告6）があり，これに基づき，目安量として2．1g以上
と定められた，n−6系の摂取については，多量摂取の危険性などに関する報告もなく，10％
を目標量として設定されている．飽和脂肪酸についてはその摂取量の増加は心筋梗塞によ
る死亡率を増加させることが知られている．
（3）炭水化物
炭水化物にはぶどう糖や果糖などの単糖類や二糖類，でんぷんなどの消化吸収されるも
のと，植物繊維や難消化性オリゴ糖などの消化吸収されないものとがある，エネルギー源
としての炭水化物の特性は，脳・神経組織・腎尿細管，酸素不足の胃格筋など通常はぶど
う糖しかエネルギー源として利用できない組織にぶどう糖を供給することである，特に脳
の基礎代謝量は多く，より多くのエネルギーを要することが知られている，炭水化物のエ
ネルギー比率は，たんぱく質と脂質の目標がそれぞれ20％未満，20∼30％であることよ
り，50∼70％エネルギーとなり，これを目標量と設定している。
妊婦・授乳婦においては，上記3大栄養素であるたんぱく質・脂質・炭水化物のエネ
一222一
2005年10月
ルギー比率は非妊娠時の成人女性と同様に摂取する基準設定となっている．
（4）その他の栄養素
ビタミンには水溶性ビタミンと脂溶性ビタミンがある．前者にはビタミンB1，B2，
B6，812，Cや葉酸などがあげられる．これらビタミンは中枢・末梢神経の機能維持や
正常な発育，生殖作用や代謝に必要な因子である，またビタミンCには抗酸化作用や心
臓血管系の疾病予防の期侍できることが示されている，したがって，妊娠時には妊娠時に
付加される推定必要エネルギー量に換算し，付加される．授乳婦には母乳として与える量
のビタミンを付加する必要があるという考え方から，付加量を加える．葉酸は，神経閉鎖
障害のリスク低減と関連することが示されており，妊婦のみならず，妊娠を予定している
女性，ある（，、は妊娠の可能性のある女性は，サプリメントとして400μg／日の摂取が勧め
られる，
一方，脂溶性ビタミンにはビタミンA，D，E，Kがあげられ，これらの欠乏と代謝・
成長障害や得・神経の発達抑制，血液凝固障害が関与する，ビタミンAは胎児への蓄積
を付加する必要性から付加することが勧められている，一方ビタミンEは妊娠時に付加
する必要性はないと考えられている．なぜなら妊娠時には血清脂質が上昇し，これに伴い
血中α一トコフェ0一ル濃度も上昇するからである。またビタミンKについては，これま
で妊婦とビタミンKに関する報告はなく，事実妊婦にお（，、てビタミンKの欠乏症がみら
れることもないので付加されない．
ミネラルでは，マグネシウムやカルシウム，リンが胃代謝に重要である，ただし，カル
シウムについては妊娠時に付加する必要はない，なぜなら妊娠時にぱ活性型ビタミンD
やエストログンなどが上昇するので，腸管からのカルシウム吸収率が上昇するからである，
微量元素の中で重要なのは鉄である．鉄はヘモグロビンや各種酵素の構成成分であり，
欠乏には留慧する必要がある，妊娠時には，胎児の成長に伴う鉄蓄積や月齊帯・胎盤中への
鉄貯蔵，赤血球の膨張による鉄需要の増加分より鉄の必要量が計算され，妊娠各時期（初
期・中期・末期）の付加量が設定されている．
3．栄養状態の評価法
栄養状態の評価法についてはさまざまな方法があるが，日本肥満学会では簡便かつ体脂
肪との相関の高いBMl［（体重（kg）／身長（m）2］を採用することを提唱している1〉，妊婦の
場合，臼本産科婦人科学会栄養問題委員会はBMlが非妊娠時あるいは妊娠初期で24以上，
中期で26以上，宋期で28以上を示す場合には＋1．OSD以上が肥満妊婦であるとしてい
る。また非妊娠時のBMlで18∼24を標準体重とし，18未満をやせとしている7〉，日本肥
満学会では成人の肥満はBMlが25以上としているので注慧を要する，
4．正常妊婦の栄養指導
正常妊婦の場合，上記の妊婦・授乳婦における栄養所要量に基づいて栄養指導を行う．
この際，臼々の栄養所要量が適正か否かを評価するための指標は体重増加である．わが国
では，報告により若干の差はあるものの10∼12kgである，ちなみに，日本産科婦人科
学会栄養問題委員会による検討では，正期産における平均体重増加量は11，46kgとして
いる7）。わが国の正常妊婦の至適体重増加量として，妊娠高血圧症候群の発症予防の概念
に墓づく勧告によると，標準体重群（BMI：18∼24）では7∼10kgとされている8）．また
Hyttenandしeitchの報告によると健康初妊婦の妊娠時の平均体重増加量は12，5kgと
している3），米国のN∂tion∂IAcademyofScienceの医学部門における妊娠時の体重
に関する勧告9〉では，やせには12，5∼18kg，正常妊婦には11．5∼16kg，肥満に対して
は7∼11．5kgが妊娠時の適正な体重増加量としτいる．ここでいうやせ・正常・肥満は
一223一
BMlでそれぞれ19，8未満，19．8∼26，26以上で定義している．またBMlが29を超え
る場合は，少なくとも6kg以上の体重増加を必要としている，American Co”ege ofOb−
stetricians and Gynecobgistslo〉もこのガイドラインを用いている，
5．肥満妊婦の栄養指導
肥満妊婦では，正常妊婦に比し，妊娠時の高血圧症を禽め，妊娠中毒症，糖代謝異常，
巨大児の発症率や帝王切開率が高くなることが知られτいる．肥満者では，食後の血糖値
がインスリン抵抗性により高値となることが特徴である．妊娠時には先述のとおり，その
末期において食後の高血糖と血中インスリン値の上昇が生理的に生じることが特徴であ
り，肥満女性の妊娠時のインスリン抵抗性の増大が考えられる．事実，肥満妊婦の血中イ
ンスリン値は非肥満妊婦に比し高いことが知られている，さらに肥満者の脂質代謝の特徴
として，高脂血症があげられるが．肥満妊婦では，妊娠によりさらにこの高脂血症が助長
されることになる，またFFAの高値はインスリンの感受性低下に関与し，インスリン抵
抗性に拍車をかけることとなる．
肥満妊婦の栄養指導に関しては、従来工ネルギー摂取を制限するべきであるという考え
方と，するべきではないという考え方がある．極端なエネルギー制限の児の長期予後に及
ぼす影響に関する根拠がないので，それが，安全であるいう根拠が確立されるまでは，現
在のところ極端なエネルギー制限はするべきではないと考えられる，特に尿中ケトン体が
陽性となるような食事制限は避けるべきである。なぜなら高濃度のケトンが児の知能に悪
影響を与える可能性があるからであるm．
先述の厚生労働省による栄養所要量の勧告では，妊婦の体格による制限は記載されてい
ない，肥満妊婦の妊娠中の体重増加量として脂肪の蓄積は既に妊娠前より十分と考えられ
るので，脂肪の蓄積量を3∼4kgと仮定した±易合．それを差し引いた体重増加量すなわち
5∼7kg程度で良いと考えられる，肥満妊婦の至適体重増加量として，先述の妊娠高血圧
症候群の発症予防勧告によると，肥満体重群（BMI：24以上）では5∼7kgとされてい
る8），
6．やせ妊婦の栄養指導
極端なやせの妊婦や体重増加量の少ない妊婦では子宮内胎児発育遅延（intrauterine
grOwth restriction l lUGR）の頻度が高くなることが知られている，1UGRでは周産期罹
病率，死亡率が高くなることに加え，胎児期の低栄養が将来の成人病，たとえば高血圧症，
2型糖尿病を含めたインスリン抵抗性症候群，脂質代謝異常や冠動脈疾患の発症に関与す
ることが示されている．
以上のことより，やせの妊婦の至適体重増加量は少なくとも正常体重妊婦よりも多い方
が望ましいが，どの程度多ければよいかに関する根拠はない，このような観点より米国で
は先述のとおり，やせの妊婦には12，5∼18kg（正常妊婦では11．5∼16kg）の増加を至適
としており，正常妊婦よりやや多めの体重増加量を設定しているものと考えられる．やせ
妊婦の至適体重増加量として，先述の妊娠高血圧症候群の発症予防勧告によると，やせ体
重群（BMl：18未満）では10∼12kgとされている9），
《参考文献》
1．日本肥満学会肥満症のてびき編集委員会編，肥満・肥満症の指導マニュアル東京：
医歯薬出版，199711−26
2．厚生労働省．日本人の食事摂取基準（2005年版）東京：第一出版、2005
3．Hytten FE，LeltCh l．The phySiOIOgy Of hUm∂n pregn∂nCy．2nd editbn．
一224一
2005年10月
Oxford：BlackweμScientific F）ubllcatiOns，1971，
4．FAO／WHO／UNU Expert Consu辻atiOn．Report on human energy require−
ments，lnterim Report，2004
5．井上五郎訳，必須アミノ酸研究委員会編：エネルギー・蛋白質の必要量，FAO／
WHO／UNU合同特別専門委員会，WHOテクニカル・レボート・シリーズ724 東
京：医歯薬出版，1994，
6。Olsen SF，Secher NJ．Low cOnsumption of seafOOd in early pregnancy as
a risk f∂ctOr fOr preterm delivery：prospectlve cohort study．BMJ20021
324：447−450
7，栄養問題委員会報告．婦人（非妊婦・妊婦）および胎児・新生児の体格現状調査，（正常
群）．日産婦誌 1988140＝1487
8．研修ノートNO，64，「妊娠中毒症」日本母性保護産婦人科医会．2001
9．lnstituteOfMedicine，Subcommittee on nutritbnal status and weight gain
in during pregnancy，Nutrition during pregnancy．Weight gain，NationaI
Academic Press，Washlngton DC，19901190：1−13
10，American College of Obstetncians and GynecOlogists l Nutrition during
F）regnancy，Technlcal Bu躊etln19931Aprll：179
11。RlzzO T，et al，Correlations between antepartum matern∂I metabo蘇sm∂d
intelligenceOfOffspring，N∈ngIJMed19911325：911一一916
〈杉山隆＊〉
＊T∂k∂shi SUGIYAMA
＊ρθ〃ηafa／0θηfθ40θρaだmθηオof Oわsオθf〃os aησGγηθoologyl
筋θUηノレθバS妙GAa伽aオθSOん00／o御θd／0ノηθ，筋θ
Key words：Pregn∂ncy・Nutritbn・Dietary・Reference Intakes
一225一
平成16年度厚生労働科学研究費補助金
（子ども家庭総合研究事業）
若い女性の食生活はこのままで良いのか？
次世代の健康を考慮に入れた栄養学・予防医学的検討
2005年3月31日発行
独立行政法人国立健康・栄養研究所
吉池信男
〒162−8636 東京都新宿区戸山1−23−1
電話：03−3203−5721、FAX：03−3202−3278

Increase in low-birth-weight infants in Japan and associated risk

Transcription

Similar documents

è¦ã/éã - æ»è³å»ç§å¤§å¦

Aç¾¤ æº¶é£èã®èååå¸ã«é¢ãã ç¬¬2å å½éååç ç©¶

Free Reading “How to” Books Embracing Open-Access

DECEMBER 2013 - Walnut Grove Buddhist Church

PHYCOLOGY

第 37 回日本微小循環学会総会

PHYCOLOGY

My Dubai Trip - Bengali Association of Tokyo Japan

âªã©ã³ãã§ã³ã»ããã¼â« - ç¬¬58åæ¥æ¬èèå¦ä¼å¦è¡ç·ä¼

PHYCOLOGY

��2014�� - ��

Analecta Nipponica

プログラムPDF - 医療系大学院高度臨床専門医養成コース

Scalaã®ç¾ç¶ã¨ä»å¾

WORKS JAPANESE COMPOSERS

日本の作曲家の作品 2005-2006