Antenatal Testing for High Risk Pregnancy

1. Antenatal Testing for High Risk Pregnancy Christopher R. Graber, MD Salina Women’s Clinic 10 Oct 2011

2. Overview • Background • Fetal physiology • Reasons to consider testing • How to test • What tests are available: NST, BPP, etc. • Which test do I choose • Test initiation and frequency • How to handle non-perfect results

3. Background • Goal of surveillance is to prevent fetal death • Identification of suspected fetal compromise  opportunity for intervention • Used for preexisting and developing maternal conditions, and developing fetal conditions • Not good for acute events • Abruption, cord events • Baseline risk of IUFD

4. 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.

5. Fetal Physiology • Fetal heart rate, level of activity, and muscular tone are sensitive to hypoxemia and acidemia • Cardiotocography, real-time sono, and fetal kick counts can point to acidemia • Extensive testing in both animal and human models shows correlations • Ex: Redistribution of fetal blood flow  decreased renal perfusion  oligohydramnios

6. Categories for Causes of Fetal Death • Fetal • Placental • Maternal

7. Reasons to Consider Testing – Maternal Conditions • Antiphospholipid syndrome • Hyperthyroidism (poorly controlled) • Hemoglobinopathies • Cyanotic heart disease • Systemic lupus erythematosus • Chronic renal disease • Type I diabetes mellitus • Hypertensive disorders

8. Reasons to Consider Testing –Pregnancy Related • Pregnancy-induced hypertension • Decreased fetal movement • Oligo-/poly- hydramnios • Intrauterine growth restriction • Postterm pregnancy • Isoimmunization (moderate to severe) • Previous fetal demise (unexplained or recurrent risk) • Multiple gestation

9. 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 BPP • Umbilical artery Doppler velocimetry

10. Fetal Movement Assessment (kick counts) • Decreased fetal movement often but not always precedes fetal death • Neither the optimal number of movements nor ideal duration for counting are defined • 10 movements in 30,60,90 min • 30 min, dark room, no distractions, try adding cold/hot drink or caffeine/calories • If abnormal then further testing • Usually NST as next step

11. Contraction Stress Test(CST or BST) • Based on the response of fetal HR to uterine contractions • Relies on premise that a suboptimally oxygenated fetus will show late decelerations due to worsening oxygenation • Test 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)

12. Interpreting CST • Negative – No late or significant variables • Positive – Late decelerations following 50% or more of the contractions (even if fewer than 3 ctx in 10 min) • Equivocal – intermittent late or variable decelerations • Unsatisfactory – fewer than 3 ctx in 10 min or an uninterpretable tracing

13. Relative Contraindications to CST • Preterm labor or high risk for preterm labor • Preterm rupture of membranes • History of extensive uterine surgery including classical cesarean delivery • Known placenta previa

14. 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 cycle • FHR tracing for up to 40 minutes • Acoustic stimulation if sleep suspected

15. Interpreting NST • Reactive (normal) • 2 or more fetal accelerations within 20 min • Acceleration: 15x15 for >32 wga, 10x10 for <32 wga • Nonreactive • Less than 2 accelerations in 20 min • Other • Variable decels ok if nonrepetitive and brief (<30s) • Prolonged decelerations associated with risk

16. Biophysical Profile(BPP) • NST combined with 4 observations on sono • Fetal breathing movements • Fetal movement • Fetal tone • Determination of amniotic fluid volume • Single vertical pocket of 2cm • AFI of >5cm • Each component is given 0 or 2 points • Total of 10 points possible

17. Interpreting BPP • Normal – 8/10 or 10/10 • Equivocal – 6/10 • Abnormal – 4/10 or less • Or oligohydramnios • BPP often performed without NST as 8/8 on sono components is reassuring

18. Modified Biophysical Profile • Placental dysfunction can result in diminished fetal renal perfusion  oligohydramnios • Long-term indicator of uteroplacental function • Modified BPP is NST plus AFI • Normal – reactive NST and AFI >5 • Abnormal if either component is not normal

19. Umbilical Artery Doppler Velocimetry • Used to assess hemodynamic components of vascular impedance • Flow velocity waveforms in the umbilical artery differ in growth-restricted fetuses • Extreme growth-restricted fetuses can show absent or reversed diastolic flow • Correlated with small-artery obliteration in placental villi and with fetal hypoxia/acidemia

20. Doppler equation . • fd= 2(ft · cosΘ · v)/c • fd = Doppler frequency shift • ft = transducer frequency • Θ = angle from incident beam to flow direction • v = velocity of target • c = speed of sound in the medium

21. Interpreting Doppler Results • S = peak systolic frequency shift value • D = peak diastolic frequency shift value • Ri = Resistance index • Abnormal: S/D ratio > 3.0 or Ri > 0.6 • Most important: note if absent or reversed end diastolic flow (AEDF or REDF)

23. Which Test to Use • Fetal kick counts – discuss with all patients • NST – reflex if decreased movement • Also use for almost all other indications • CST – if concerns for uteroplacental flow • BPP – reflex if nonreactive NST • Also use for almost all other indications • Doppler – best to monitor growth restriction

24. When to Schedule Testing • Start testing to balance • Prognosis for neonatal survival • Severity of maternal disease • Risk of fetal death • Potential for iatrogenic prematurity due to tests • Most patients should likely start at 32-34 wga • With severe disease or multiple risks, consider start at 26-28 wga

25. 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 pregnancy • Type I DM • IUGR • Pregnancy-induced hypertension • Consider add’l testing if medical deterioration

26. Interpreting Results • Normal results are highly reassuring • NPV: 99.8% for NST, 99.9% for CST, BPP, mBPP • For abnormal tests, always consider the overall clinical picture • Stabilizing maternal condition may help fetus • BPP of 6/10 is equivocal, repeat in 24 hours • Consider maternal corticosteroids • BPP of 4 or less usually indicates delivery • Oligohydramnios always means more evaluation

27. Umbilical Doppler Utility • Usually used only for IUGR • Weekly testing if normal • Consider more frequently if s/d ratio rises • Consider daily testing if AEDF • Consider delivery if REDF • Doppler has been used on middle cerebral artery for fetal anemia (isoimm or TORCH) • Higher flow = fewer RBCs

28. Oligohydramnios • Normal: single pocket >2cm or AFI >5cm • Evaluate for rupture of membranes • If term or postterm, consider delivery • If preterm, repeat fluid assessment • Close monitoring recommended

29. Questions?