Maternal-Fetal Medicine and Perinatal Outcomes
What this domain tests
Maternal–fetal medicine items test fetal surveillance interpretation, growth restriction, preterm birth interventions, alloimmunization, and prenatal diagnosis.
Core rules
- NST. Reactive at ≥32 weeks = two accelerations of ≥15 bpm lasting ≥15 seconds in 20 minutes; before 32 weeks use 10 bpm/10 seconds. Category III (absent variability with decelerations, sinusoidal, or bradycardia) needs immediate action.
- BPP. Eight points; ≥8 normal, 6 equivocal, ≤4 warrants delivery. Oligohydramnios: AFI ≤5 cm or deepest pocket ≤2 cm.
- Fetal growth restriction. EFW <10th percentile with abnormal umbilical artery Doppler. Absent end-diastolic flow: admit, give steroids, deliver around 32–34 weeks; reversed flow earlier.
- Preterm birth. Betamethasone 12 mg IM twice 24 hours apart at 24–34 weeks. Magnesium sulfate for neuroprotection before 32 weeks: 4 g load, then 1 g/h.
- Rh disease. Give anti-D 300 µg at 28 weeks and within 72 hours of delivery of an Rh-positive infant; also after amniocentesis, ectopic pregnancy, and threatened abortion.
- Sinusoidal pattern suggests severe fetal anemia - arrange immediate delivery and cord blood studies.
Worked example
At 31 weeks a woman reports reduced fetal movements. The NST shows late decelerations with minimal variability - category III. Do not repeat the trace in an hour; position her left lateral, give oxygen, stop oxytocin if running, and proceed to cesarean delivery after steroids if time allows.
Traps
Calling a 30-week NST non-reactive using 15-bpm criteria; treating oligohydramnios with bed rest instead of investigating membranes and growth; omitting anti-D after a first-trimester loss; delaying delivery for a category III trace.