Antenatal Testing for High Risk Pregnancy

Christopher R. Graber, MDSalina Women’s Clinic10 Oct 2011

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

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

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.

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

Categories for Causes of Fetal Death

FetalPlacentalMaternal

Reasons to Consider Testing – Maternal Conditions

Antiphospholipid syndromeHyperthyroidism (poorly controlled)HemoglobinopathiesCyanotic heart diseaseSystemic lupus erythematosusChronic renal diseaseType I diabetes mellitusHypertensive disorders

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

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

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

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)

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

Oligohydramnios

Normal: single pocket >2cm or AFI >5cmEvaluate for rupture of membranesIf term or postterm, consider deliveryIf preterm, repeat fluid assessment

Close monitoring recommended

Questions?