Maternal-Fetal Medicine and Fetal Assessment
Domain 9 - Maternal-Fetal Medicine and Fetal Assessment
This domain tests antepartum fetal surveillance, growth assessment and Doppler interpretation. Questions ask you to classify a test as normal, equivocal or abnormal and to decide the timing of delivery.
Core rules
- CTG/NST: reactive if two accelerations ≥15 bpm lasting 15 seconds within 20 minutes (from 32 weeks; before 32 weeks use 10 bpm/10 seconds).
- Biophysical profile (max 10): NST, fetal breathing, movement, tone, and amniotic fluid volume. Score 8–10 normal, 6 equivocal (repeat), ≤4 abnormal - deliver after steroids if preterm.
- Amniotic fluid: AFI ≤5 cm or single deepest pocket <2 cm = oligohydramnios; AFI >24 cm = polyhydramnios.
- Umbilical artery Doppler: rising systolic/diastolic ratio → absent end-diastolic flow (deliver around 32–34 weeks) → reversed end-diastolic flow (deliver around 30–32 weeks after steroids).
- Fetal anaemia: middle cerebral artery peak systolic velocity >1.5 MoM.
- FGR: estimated fetal weight <10th centile with abnormal Doppler or <3rd centile alone; distinguish constitutionally small fetuses.
- Corticosteroids at 24–34 weeks; magnesium sulfate for neuroprotection if delivery is expected before 32 weeks.
- Bishop score ≥6 indicates a favourable cervix for induction.
Worked example
At 33 weeks with reduced movements, the NST is non-reactive and the BPP scores 6 (fluid and tone only). The score is equivocal, so repeat after positioning and glucose; if it remains ≤6 with abnormal umbilical Doppler, give dexamethasone, magnesium sulfate and deliver by caesarean.
Traps
Using the 15 bpm acceleration criterion at 28 weeks; calling a BPP of 6 abnormal and delivering immediately without steroids; diagnosing FGR from abdominal circumference alone; forgetting that AFI uses four quadrants while the deepest pocket is a single measurement.