Obstetrics – high-risk pregnancy and maternal-fetal medicine
Introduction
Maternal-fetal medicine tests risk stratification, hypertensive disease, diabetes, preterm birth, fetal growth restriction, alloimmunisation and multifetal pregnancy - with emphasis on the threshold decisions that change management.
Hypertensive disease
- Preeclampsia: new BP ≥140/90 after 20 weeks plus proteinuria ≥300 mg/24 h (protein/creatinine ≥30 mg/mmol) or maternal organ dysfunction - platelets <100 ×10⁹/L, creatinine >90 µmol/L, doubled transaminases, pulmonary oedema, neurological symptoms.
- Severe features: BP ≥160/110, headache or visual disturbance, right upper quadrant pain, HELLP syndrome.
- Proteinuria is not mandatory once organ dysfunction is documented.
- Prevention: aspirin 100–150 mg from 12–16 weeks in women with previous preeclampsia, chronic hypertension, renal disease, diabetes or twins.
- Eclampsia: magnesium sulphate 4–6 g IV loading over 20 minutes then 1–2 g/h, monitoring reflexes, respiratory rate and diuresis.
Diabetes
- Gestational diabetes is diagnosed by 75-g oGTT at 24–28 weeks with IADPSG cut-offs: fasting 5.1–6.9, 60 min ≥10.0, 120 min 8.5–11.0 mmol/L; one abnormal value suffices.
- Pre-existing diabetes needs preconception HbA1c optimisation, folic acid 5 mg, anomaly scan and fetal echocardiography.
Preterm birth and growth
- Antenatal corticosteroids at 24–34 weeks (betamethasone 12 mg twice, 24 hours apart).
- Magnesium sulphate for neuroprotection when delivery is expected before 32 weeks.
- Fetal growth restriction: estimated weight below the 10th centile with abnormal umbilical artery Doppler; steroid cover before 34 weeks and delivery guided by CTG and Doppler.
Worked example
A 34-year-old at 33+4 weeks has BP 168/110, 3+ proteinuria, platelets 92 ×10⁹/L and ALT 3.5 µkat/L with headache. This is preeclampsia with severe features, not gestational hypertension: the platelet count and transaminases establish organ involvement. Admit her, start labetalol or nifedipine targeting 130–140/80–90, give magnesium sulphate for seizure prophylaxis, give betamethasone, and plan delivery after the steroid window - caesarean section if the cervix is unfavourable.
Traps
- Diagnosing preeclampsia before 20 weeks (think hydatidiform mole or secondary hypertension).
- Over-lowering blood pressure and compromising uteroplacental perfusion.
- Delivering for severe preeclampsia without magnesium prophylaxis.
- Calling a small fetus growth restricted on centile alone, without Doppler.