Ultrasonographic diagnosis and management of fetal abnormality in

Pferdeheilkunde15 (1999) 6 (November/Dezemb,er)
618-621
Ultrasonographic
diagnosisand managementof fetal
abnormalityin the mare in late pregnancy
A.J. Mccladdery
Rossdaleand Partners,BeauiortCottageStables,HighStreet,Newmarket,
UK
Summary
Pregnantmares suspected of havinga complicationcan be examinedby transabdomnal ultrasonographyto determinethe state of fetal
well being. Reasonsincludeprematuremammarydevelopmentand lactation,vulvaldischarge,severematernaldisease,marked abdominal
enlargementand prolongedgestation.Usefulmeasurementsincludefetal aortic diameter,fetal heart rate and activity,fetal fluid depth and
consistency,utero placentalthicknessand contact, fetal positionand presentationand the presenceof fetal breathingmovements.The
combined utero-placentalthicknesscan also be measuredtransrectally.Combinlngthese parametersnto a biophysicalprofilemay predict
with greateraccuracythe finalfetal outcome.Any inaccuracymay be relatedto problemsthat developduring deliverysuch as dystociaand
prematureplacentalseparationwhich were not presentpreviously.In one largeseriesof 122 cases,61% of fetal scans were normalof these
supposedlynormal pregnancies79% delivereda normaifoal, 39% of scans were abnormalof these '19%subsequentlydelivereda normal
loa . Once the state of fetal well-beinghas been assessedmanagementis directedat treatingthe maternaldiseaseappropriately,combined
with speciflctreatmentsincludingthe use of antibioticsin placentitisand progesteronesupplementatlon.Fetaladrenocorticalmaturationis
essentialto new born foal viability.Becauseit occurs at the very end of gestationtherapyshould be aimed at maintaininga stable 'in utero'
environmentcapableof supportingthe fetus untilthis has been achieved.However,due to suspectedimpendingfetal death prematuredeli
very of the fetus may be necessary.Increasingthe speed of fetaladrenocorticalmaturationby intra-fetaladministrationof ACTH, in selected
cases, particularlywhere maternaldeath is imminentand full terrn is distant should be consideredcarefullyas the techniqueis not without
risk.
Keywords:
pregnancy,fetalmaturation
ultrasonography,
horse,fetalassessment,
Ultrasonographische Diagnostik und Behandlung fötaler Fehlformationenbei Stuten in der späten Graviditätsphase
Bei Verdachtauf e nen komplikativenVerlaufder Trächtigkeitkann der Vitalitätszustand
des Föten durch transabdominaleUltrasonographie
bestimmtwerden. Indikationenfür dlese Untersuchungensind vorzeitlgeEuteranbildung
und Laktation,Genitalausfluss,
schwerwiegendeErkrankungder Mutterstute,autfälligerBauchumfangund verlängerteTrächtigkeit.BrauchbareUntersuchungsverfahren
schliessenden fötalen
Aortendurchmesser,
fötaleHerlrequenz und Aktivität,Ausmassund Konsistenzder Fruchtwässer,Dickeder Utero-Plazentaschicht
und deren Kontakt,die fetaleStellungund Lage und das VorhandenseinfötalerAtmungsintentionen
ein. Die kombinierteutero-plazentale
Schichtgemessenwerden. Die Kombinationdieser Parameterin einem biophysikali
dicke kann ebenfallsüber die transrektaleUltrasonographie
schen Profilkann zu einergrößerenprognostischenGenauigkeitbezüglichdes weiterenFortgangsder Trächtigkeitund der VitalitätsChancen des Fohlensführen. Fehlprognosennach Anwendungeines solchenUntersuchungsprofils
dürften auf Problemezurückzuführensein,
die sich erst während des Geburtsablaufsergebenwie z.B. Dystokienoder vorzeitigePlazentaablösung,
die vorher nicht erkannt werden
KOnnen.
In einer großen Serievon 122 Fällenfötaler Untersuchungenwurden 6'1%als normal eingestutt,von denen 79% normaleFohlengeboren
wurden. In 39% der untersuchtenLe besfrüchtewurde eine abnormaleFruchtanlagediagnostizieft,von denen in 197oder Fälleein normales
Fohlengeborenwurde. Sobald der fötaleVitalitätsstatus
festgestelltist, richtetsich die Behandlungmöglichstkausativgegen die mütterliche
Erkrankungin Kombinationmit spezfischerTherapie,die dle Applikationvon Antibiotikain Fällenvon Plazentitisund die Supplementierung
von Progestagenenbeinhaltet.Die fetale,adrenocortikalgesteuerteAusreifungist essentiellwichtig für die Vitalitätdes Neugeborenen.Da
dies in den letäen Phasender Graviditäterfolgt,sollteeine Therapiedie Aufrechterhaltung
eines stabilenendouterinenMilieus,das zur Erhaltungdes Fötus' in der Lage ist, zum Ziel haben.Jedoch kann bei unmittelbarzu ervvartendemFruchttoddie vorzeitigeGeburt des Föten
erforderlichsein. Die Beschleunigungder fötalenReifungdurch intrafötaleApplikationvon ACTH in besonderenFällen,z.B. bei bevorstehendem mütterlichemTod und noch nicht en'eichtemAbfohlterminbedad sorgfältigerAbwägung,da diese Behandlungstechnik
nicht ohne Risiko ist.
Schlüsselwörter
Ultrasonographie,
Pferd,Fetusuntersuchung
und -bewertung,Trächtigkeit,fetaleReifung
lntroduction
Ultrasonographic
examinationis the most usefultechnique
for assessingfetalwell-beingin maresthat developcomplications in late pregnancy(Adams-Brendemuehl
and Pipers,
1987; McGladdery, 1998). Although, in late pregnancy
transcutaneousor transabdominalexaminationprovides
the best visualisationof the fetus, transrectalexamination
will allow more detailedexaminationof the head and neck
618
of the fetus and placentaat the cervicalpole. Indications
for assessmentof fetal well being includeprematuremammary developmentand lactation,vaginaldischarge,excessive abdominalenlargement,a previousmaternalhistoryof
dystociaand/or prematureplacentalseparation,a previous
historyof a foal sufferingfrom prematurityor sepsis,severe
maternalillness(eg. fever/endotoxaemia)
or disease cauPferdeheilkunde
15
A.J. McGladdery
sing marked disabilityor debilitation(eg. severemalnutrition, chronic severe lameness/laminitis
or severeneurological disease),abdominal pain (particularlyof reproductive
origin)and prolonged gestation.Followingassessmentof
the fetus, a managementplan can be formulated,in conjunctionwith any maternaltherapy,for the best care of the
pregnancyuntil full term. Becausethe major organs of the
equine fetus are requiredto undergo criticalmaturational
processesduring the last days of pregnancy,fetal survival
at less than 295-300 days of gestation is rare. Even after
this time, deliveryof a maturefetus is not cedain,and problems of dysmaturityare frequentlyencountered.However,
fetoplacentalstress, in some circumstances(eg. placentitis), may cause sufficientmaturityof the fetal adrenalcortex
to occur that increasedviabilityof the foal is possibleeven
at early gestationalages. For this reason, most management regimes are designed to enhance, if possible,fetal
viabilityin utero. However,if imminentfetal demise is suspected,then inductionof parturitionand deliveryof the foal,
may become essential.
Diagnosis
Ultrasonographicexaminationof the fetus may be performed using eithera linearor sector transducer.Normally
a 3.5 MHz or lower frequencytransduceris used for general surveyingof the fetus and placentawith more detailed
m ade us i n ga 5 M H z o r 7 .5 M H z tra n sducer.
e xa mi nat ions
Because sedative drugs will affect fetal activity and fetal
heart rate and therefore limit the accuracy of fetal assessment, sedation of the mare should be avoided. During a
routinefetal ultrasoundexamination,the mare's ventralabdomen should be systematicallyexaminedfrom her sternum to her mammarygland and on eitherside of midlineto
the levelof the flank fold. In late gestationthe fetus will, in
nearlyall cases, be in anteriorpresentationeitherin dorsal
or dorsolateralrecumbency.The fetal thorax is usuallythe
most easilyidentifiedstructure,the fetal heart can be readily identifiedcontractingin the cranialthorax with the major
blood vesselspassingcaudally,the aorta lying next to the
spinalvertebrae.The diaphragmcan be recognisedseparating the abdominaland thoracic cavitiesand fetal breathing movementsmay be noted. In the fetal abdomen,the
fluidfilled(anechoic)stomach,kidneysand liverare all easil y i d e n t if ied.
T he um b i l i c acl o rd (2 u mb i l i c aal rte ri e s,u mbi l i cal vein, urachus),can be seen floating within the fetal
fluids.The amnion forms a brightly,echogenicmembrane
that divides the amniotic cavity from the allantoiccavity.
The placentacan be recognisedborderingthe allantoiccavity, the uterus and placentaform a combined structure
which is homogeneousin appearanceand normallyless
th a n 2 c m in t hic k nes s .
Severaldifferentmeasurementsof the fetus have been made
during mid and late gestationwith the aim of predicting
fetal size relativeto gestationalage. The most consistently
useful has proved to be aortic diameter (measuredat the
caudalborderof the heart.Althouqh,initialstudieslAdamsPferdeheilkunde
15
Brendemuehland Pipers, 1987) of fetal aortic diameter did
not find a strong correlationwith neonatalfoal weight and
were not consideredaccuratein detectingsmall or impoverished fetuses. A more recent study (Reef et al., 1996)
has found both the fetal aortic and thoracicdiameterto be
accuratein predictingthe smallfetus in a high risk pregnancy. Besidesdetectingthe thicknessof the combineduterus
and placenta, areas of placental separation may also be
noted. The fetal fluidsare normallyanechoic,however,the
allantoicfluid in late gestationmay contain numerous hyperechoicfoci. During fetal distress,meconium diarrhoea
may lead to an increasednumber and size of free floating
oafticleswithin the amnioticfluid.This must be differentiated from the hippomane,which is an easily recognised
oval,echogenic,concentricstructureseen floatingin the allantoicfluid.The depth of the fluid pool surroundingthe fetus can be measuredto assessthe overalltotal volume of
fetal fluid both amnioticand allantoic.Other measurements
that are useful,includefetal heart rate (eithermeasureddirectlyby countingthe numberof fetal heartbeatsover a defined periodof time or alternatively,
the R-R intervalcan be
calculatedby M mode scanningof the fetal heart),Numerous workers have documentedthe decreasingfetal heart
rate that occurs with increasinggestationalage related to
increasingparasympathetictone in the developingfetus.
Transientfetal heart rate accelerationsare associatedwith
fetal movement and activity in the normally developing
fetus. Assessmentof fetal activityis also usefuland during
a routinescan of 20-30 minutes duration it is unusualto
see periodsof more than a few minutesof fetal inactivityor
fetal sleep.Limb, head and neck and rotationalmovements
aroundthe fetal body axis can be visualised.
Two groups of
workers (Adams-Brendemuehland Pipers, 1987; Reef et
al., 7995)have repoded normalvaluesfor the late gestational fetus. Both have developeda biophysicalprofileto detect fetal abnormalitybased on a scoring system involving
severaldifferentmeasurements(Reefet al., 1996).
The following ultrasoundfindings have been associated
with a suspectedor proven abnormalityof the fetus. Fetal
heart rates,eithermuch higheror much lower than expected for fetal gestationalage, were associated with abnormality.An inactivefetus with a resting heart rate of greater
than 100 beats or a fetus with a heart rate of less than 50
beats was consistentlyassociatedwith abnormality.Prolonged periodsof fetal inactivitywere consistentlyassociated with abnormality.However,in a smallnumber of cases,
abrupt markedlyexcessiveactivitywas also associatedwith
abnormality.Besidesfetal activity,fetal tone has also been
assessedand when absentwas associatedwith abnormality. Reefet al. (7996)consistentlyfound that aorticdiameter
correlatedwell with foal weight in both normaland complicated pregnancies.Not all clinicalworkers have supported
this finding.Reducedquantities,particularly
of allantoicfluid
were associatedwith abnormality,as was increasedechogencity of the fetal fluids. Where abdominalenlargement
occurs in late pregnancy,ultrasoundexaminationmay reveal fetal hydrops with excessiveproductionof fetal fluid,
eitherallantoicor amnioticin origin.In these cases,on rec-
619
Ultrasonographic
diagnosisand managementof fetalabnormality
in the marein latepregnancy
tal palpation,it is normallyimpossrbleto palpatethe fetus.
Transabdominalscan finds that the fetus is surroundedby
a much largervolumeof fluidthan normal.In one case a fetus also had an omphalocelewith herniated intestines,
which were visibleon ultrasoundexamination,As has been
mentioned previously,examinationof the uteroplacental
unit may revealthickening,focal increasedechogencityassociatedwith calcification
and olacentalseoaration.
Measurementof the combinedthicknessof the uterusand
placenta (CTUP)has recently been reported by transrectal
measurementat the ventralaspect of the uterinebody and
near the cervical-placentaljunction (Troedsson et al.,
1997).The normalCTUP is reportedto be less than 7 mm
before 300 days of gestation,Mares at risk of placentalfail u re h a ve CT UP ' s> B mm a t2 7 1 -3 0 0 d a y s a n d > 1 O mm
301-330 days. The presenceof fetal breathingmovements
is not associatedwith abnormality.Unfodunately,the presence of one abnormal measurementalone is not always
accurate in indicatingthe probabilityof a poor fetal outcome. For this reason biophysicalprofilinghas been used
to predict fetal outcome. Reef et al. (7996) have developed
a biophysicalprofileusingthe followingvariables,fetal heart
rate, aorlic diameter, fetal activity level, utero-placental
thickness, uteroplacentalcontact and maximal fetal fluid
deoth. A score of 2 for normaland 0 for abnormalare assignedto each variableand the 6 variablesare summed to
give a biophysicalprofilescore that rangesfrom O to 12. lf
a fetus had a biophysicalprofilescore that was lessthan or
equalto B it was assuredof a negativeoutcome,However,
a maximal score was not an assuranceof normality.In
most cases, the reason for an abnormal outcome with a
maximum biophysicalprofile score was associated with
problemsthat developedduringdeliveryincludingpremature
placentalseparation,dystociaand failureof the chorioallantois to rupture.ln a large scale study by Reimer(7997)ot
122 mares that had complicated pregnancies,61% of
pregnancieswere consideredto be normalfollowingultrasound examination(Biophysicalprofilingwas not used),Of
these, 79%owere associatedwith a normal foal at delivery.
160/oof foals resultingfrom pregnancieswith a normalultrasound examinationwere stillborn,died or were euthanised
before48 hours.Some of these caseswere eitherassociated with dystociaor caesareansectiondue to an ultimately
fatal disease of the mare, The vast majority of mares with
prolongedgestationshad normal ultrasoundexaminations
and a normalfetaloutcome.In one case, in the author'sexperience,of a prolongedgestationassociatedwith abnormal fetal outcome.The fetus was noted to be consistently
inactive,on repeatedultrasoundexamination,with a bradycardia and absence of fetal heart rate variability,The fetus
was eventuallystillbornand found to be congenitallyabnormal with anencephalyand an open defect in the cranium.In
Reimer'ssurvey,in 39% of mare's fetal ultrasoundexaminationswere consideredto be abnormal.In these cases,
abnormalfindingsincludedthickenedplacenta,echogenic
retroplacentalfluid and placentalseparation(subsequently
found to be mucoid, purulentor haemorrhagicat pafturition) both fetal hydrops and reduced quantities of
620
allantoic/amniotic
fluid, fetal death, breech presentationin
late pregnancy,twin pregnancy,fetal ascitesand omphalolow or elevatedheart rates and
cele, Also, inappropriately
cardiacarrhythmiaswere also noted. In two cases fetuses
were noticed to have sudden bouts of abnormally,excessive activitycharacterisedby apparentlyviolentactivitywith
periodsof abrupt cessation.In both cases the foalsdied. In
several cases inactivitywas associated with a poor fetal
outcome. However,one foal was found to be completely
inactiveon severalultrasoundexaminations,yet at delivery
was normal. 19% of abnormal ultrasound examinations
were associatedwith a normalfoal. Duringfetal evaluation,
peritonitis,haemoperitoneum
and broad ligamenthaemorrhage were identifiedin three mares.
Management
Therapyfor mares with complicationsin late pregnancyis
directedprimarilyat appropriatetreatmentof the maternal
disease. Mares with placentitismay be treated with systemic antimicrobials
chosen dependingon the antibioticsensitivityof the organismcultured.Experimental
evidencehas
so far indicatedthat, normally,only trimethoprimcrosses
the placentato the fetal circulationhowever, in cases of
placentitisinflammationof the chorioallantoismay allow
greaterand more variedtransferof drugs. Although,a variety of maternal conditions particularlythose associated
with endotoxaemiamay result in large increasesin uterine
prostaglandins
capableof causingabortionthere is no evidence that the use of Nonsteroidaldrugs, which inhibit
cycloxygenases,are able to prevent abortion. Similarly,the
use of exogenousprogesteronetherapy (eg. altrenogest),
which is widespread,may possiblycause increaseduterine
quiescencewith reducedmyometrialactivityand increased
cervicalintegrity,Some cliniciansadvocatethe use of tocolytic drugs such as clenbuterolwhich relax the myometrium. Both progesteroneand altrenogestdo appear able to
block the effect of cloprostenolinduced abortionand this,
effect on prostaglandins,is an important reason for their
use in complicatedpregnancies.
Regular reassessmentof the complicated pregnancy as
term approachesis helpfulto allow preparationfor delivery
of a compromised foal. In some cases the possibility
of speedingup fetal maturationto allow early deliveryof a
viablefoal comparedto that normallyexpectedfor the gestationalage would be a great advantage.Studies in research oonies have shown that it is oossibleto advance
gestationof a viablefoal by direct fetal therapy.The author
has experienceof treating 3 clinicalcases with fetal ACTH
injectionsto induceprecociousfetal adrenocorticalmaturation. The first case was a TB mare with severe,acute laminitis,Fetalinjectionsof 1 mg of depot ACTH were givenvia
an ultrasound-guided
techniqueat 309 days and dailyfrom
337-339 days of gestationand deliverywas inducedat 341
days. Although,the foal did require some hospitalisation
due to dysmaturityit did survive.The second case involved
a TB mare with severeemaciationdue to eosinoohilicoraPferdeheilkunde
15
A.J. McGladderv
VirginiaB. Reef, Wendy E. Vaala, Leila T. Worth, Patricia L. Sertich,
nulomatousenteritis.Fetalinjectionswere givenat 368 and
PamelaA. Spencerand BarbaraHammett(1995):Transabdominal
370 days because of the mare's physicalcondition and
ultrasonographic
evaluationof the fetus and intrauterineenvironlack of mammarydevelopment.Prematureplacentalsepament in healthymares during late gestation.Vet. Radiol.Ultrasoration at 371-372 days resultedin fetal death during deliu n d .3 6 , 5 3 3 - 5 4 1 .
very, In the third case a TB mare with a septictenosynovitis VirginiaB. Reef, Wendy E. Vaala, Leila T. Worth, Patrtcia L. Sertich
and PamelaA. Spencer(1996):Ultrasonographic
assessmentof fecausingsevereunilateralhindlimblamenessunderwentfetal
gestation:
tal
wellbeing
late
during
development
of an equinebiogestation
injectionsdaily at 314-316 days of
and delivery
physicalprofile,Equinevet.J. 28,200-208.
by caesarian section at 331 days again resulted in a
JohannaM. Reimer(1997):Use of transcutaneous
in
ultrasonography
dysmaturefoal which although,it surviveduntil 1O days of
complicatedlatter-middle
to lategestationpregnanciesin the mare:
age was then finallyeuthaniseddue to a septicjoint. In two
122 cases.43rdAnn.AAEPProceedings
Vol.43,259-261.
of these cases prematuredeliveryof a viablefoal appeared
M.H.T. Troedsson,CatherineD. Renaudin,W.W.Zent and J.V Steiner
(1997):Transrectal
ultrasonography
of the placentain normalmares
improveddue to fetal injection.However,the procedureis
with pendingabortion:a fieldstudy.43rd Ann. AAEPProceedings
not without risk and abortionsand placentallesionswere
Vol,43,256-258.
associatedwith the fetal injectionsin some of the research
ponies injected.In view of this, the use of this technique
should be consideredcarefullyand limitedto cases where
fetal maturationis essentialbecause of the imminentdemise of the mare.
Literature
Caroline
and F.S.Prpers(1987):Antepartum
S. Adams-Brendemuehl
evaluations
of theequine
fetus.J. Reprod.
Fert.Suppl.35,563-73.
(1998):
A.J.McGladdery
FetalUltrasonography.
Equine
Diagnostic
UlpuEditedby N.W.Rantanen
trasonography
andA.O.McKinnon,
W, illiamand
s Wi l k i n B
s ,a l trmo re
b l i sher
U SA
, 1, 7 1 -1 8 0 .
F. E. DudanandAbigailL. Fowden
JenniferC. Ousey,P.D.Rossdale,
(1999):
Theeffectsof intra-fetal
ACTHadministration
on theoutcomeof pregnancy
inthemare,Reprod.
Fert.Dev.
10,(4).
Andrew J. McGladdery
Beauforl Cottage Stab/es
High Street
Newmarket
Suffolk,CBB BJS
UK
tel.:+44 1638663 150
fax +441 1638660 157
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