Antenatal Testing for High Risk Pregnancy
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Antenatal Testing for High Risk Pregnancy
Christopher R. Graber, MDSalina Women’s Clinic10 Oct 2011
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Overview
BackgroundFetal physiologyReasons to consider testingHow to test
What tests are available: NST, BPP, etc.Which test do I chooseTest initiation and frequencyHow to handle non-perfect results
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Background
Goal of surveillance is to prevent fetal deathIdentification of suspected fetal compromise opportunity for interventionUsed for preexisting and developing maternal conditions, and developing fetal conditionsNot good for acute events
Abruption, cord eventsBaseline risk of IUFD
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Baseline risk of IUFD
Perinatal mortality and gestational age. Open circles represent the cumulative probability of perinatal death × 1000. Closed circles represent perinatal mortality rate per 1000 births.
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Fetal Physiology
Fetal heart rate, level of activity, and muscular tone are sensitive to hypoxemia and acidemiaCardiotocography, real-time sono, and fetal kick counts can point to acidemiaExtensive testing in both animal and human models shows correlationsEx: Redistribution of fetal blood flow decreased renal perfusion oligohydramnios
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Categories for Causes of Fetal Death
FetalPlacentalMaternal
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Reasons to Consider Testing – Maternal Conditions
Antiphospholipid syndromeHyperthyroidism (poorly controlled)HemoglobinopathiesCyanotic heart diseaseSystemic lupus erythematosusChronic renal diseaseType I diabetes mellitusHypertensive disorders
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Reasons to Consider Testing –Pregnancy Related
Pregnancy-induced hypertensionDecreased fetal movementOligo-/poly- hydramniosIntrauterine growth restrictionPostterm pregnancyIsoimmunization (moderate to severe)Previous fetal demise (unexplained or recurrent risk)Multiple gestation
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How to Test – Tests Available
Fetal movement assessment (kick counts)Contraction stress test (CST)
Breast stimulation stress test (BST)Non-stress test (CST)Biophysical profile (BPP)
Modified BPPUmbilical artery Doppler velocimetry
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Fetal Movement Assessment (kick counts)
Decreased fetal movement often but not always precedes fetal deathNeither the optimal number of movements nor ideal duration for counting are defined
10 movements in 30,60,90 min30 min, dark room, no distractions, try adding cold/hot drink or caffeine/calories
If abnormal then further testingUsually NST as next step
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Contraction Stress Test(CST or BST)
Based on the response of fetal HR to uterine contractionsRelies on premise that a suboptimally oxygenated fetus will show late decelerations due to worsening oxygenationTest is administered with at least 3 contractions of 40 sec duration in 10 min Induce contractions with breast stimulation or pitocin (0.5 mU/min, then double q 20 min)
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Interpreting CST
Negative – No late or significant variablesPositive – Late decelerations following 50% or more of the contractions (even if fewer than 3 ctx in 10 min)Equivocal – intermittent late or variable decelerationsUnsatisfactory – fewer than 3 ctx in 10 min or an uninterpretable tracing
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Relative Contraindications to CST
Preterm labor or high risk for preterm laborPreterm rupture of membranesHistory of extensive uterine surgery including classical cesarean deliveryKnown placenta previa
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Nonstress Test(NST)
Based on premise that non-acidotic fetus will show fetal heart rate accelerations with movement (reactivity)Loss of reactivity is most commonly associated with fetal sleep cycleFHR tracing for up to 40 minutesAcoustic stimulation if sleep suspected
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Interpreting NST
Reactive (normal)2 or more fetal accelerations within 20 min
Acceleration: 15x15 for >32 wga, 10x10 for <32 wga
NonreactiveLess than 2 accelerations in 20 min
OtherVariable decels ok if nonrepetitive and brief (<30s)Prolonged decelerations associated with risk
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Biophysical Profile(BPP)
NST combined with 4 observations on sonoFetal breathing movementsFetal movementFetal toneDetermination of amniotic fluid volume
Single vertical pocket of 2cmAFI of >5cm
Each component is given 0 or 2 pointsTotal of 10 points possible
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Interpreting BPP
Normal – 8/10 or 10/10 Equivocal – 6/10Abnormal – 4/10 or less
Or oligohydramnios
BPP often performed without NST as 8/8 on sono components is reassuring
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Modified Biophysical Profile
Placental dysfunction can result in diminished fetal renal perfusion oligohydramnios
Long-term indicator of uteroplacental functionModified BPP is NST plus AFI
Normal – reactive NST and AFI >5Abnormal if either component is not normal
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Umbilical Artery Doppler Velocimetry
Used to assess hemodynamic components of vascular impedanceFlow velocity waveforms in the umbilical artery differ in growth-restricted fetusesExtreme growth-restricted fetuses can show absent or reversed diastolic flow
Correlated with small-artery obliteration in placental villi and with fetal hypoxia/acidemia
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Doppler equation .
fd= 2(ft · cos Θ · v)/c
fd = Doppler frequency shiftft = transducer frequencyΘ = angle from incident beam to flow directionv = velocity of targetc = speed of sound in the medium
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Interpreting Doppler Results
S = peak systolic frequency shift valueD = peak diastolic frequency shift valueRi = Resistance indexAbnormal: S/D ratio > 3.0 or Ri > 0.6
Most important: note if absent or reversed end diastolic flow (AEDF or REDF)
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Which Test to Use
Fetal kick counts – discuss with all patientsNST – reflex if decreased movement
Also use for almost all other indicationsCST – if concerns for uteroplacental flowBPP – reflex if nonreactive NST
Also use for almost all other indicationsDoppler – best to monitor growth restriction
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When to Schedule Testing
Start testing to balancePrognosis for neonatal survivalSeverity of maternal diseaseRisk of fetal deathPotential for iatrogenic prematurity due to tests
Most patients should likely start at 32-34 wgaWith severe disease or multiple risks, consider start at 26-28 wga
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Testing Schedule
NST for decreased fetal movement – prn If stable maternal medical condition – consider weekly testing (NST, BPP, mBPP)Consider twice weekly testing for
Postterm pregnancyType I DMIUGRPregnancy-induced hypertension
Consider add’l testing if medical deterioration
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Interpreting Results
Normal results are highly reassuringNPV: 99.8% for NST, 99.9% for CST, BPP, mBPP
For abnormal tests, always consider the overall clinical picture
Stabilizing maternal condition may help fetusBPP of 6/10 is equivocal, repeat in 24 hours
Consider maternal corticosteroidsBPP of 4 or less usually indicates delivery
Oligohydramnios always means more evaluation
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Umbilical Doppler Utility
Usually used only for IUGRWeekly testing if normal
Consider more frequently if s/d ratio risesConsider daily testing if AEDFConsider delivery if REDF
Doppler has been used on middle cerebral artery for fetal anemia (isoimm or TORCH)
Higher flow = fewer RBCs
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Oligohydramnios
Normal: single pocket >2cm or AFI >5cmEvaluate for rupture of membranesIf term or postterm, consider deliveryIf preterm, repeat fluid assessment
Close monitoring recommended
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Questions?