Obstetrics and Gynecology: Pregnancy Physiology and Obstetric Emergencies
The Obstetrics and Gynecology domain tests the physiology of pregnancy, antenatal and intrapartum care, obstetric emergencies, and core gynaecological conditions including contraception and cancer screening.
Core rules
- Menstrual cycle: oestrogen peaks before the LH surge; ovulation occurs about 14 days before the next period; the luteal phase is relatively constant.
- Contraception: combined hormonal methods are contraindicated with migraine with aura, smoking over 35, uncontrolled hypertension and prior VTE; progestogen-only and long-acting reversible methods have fewer restrictions.
- Antenatal care: folic acid 400 micrograms preconception, dating scan at 11–14 weeks, anomaly scan at 18–20 weeks, gestational diabetes screening at 24–28 weeks.
- Labour: first stage to full dilatation, second to delivery, third to placental expulsion. Umbilical cord prolapse - call for help, elevate the presenting part, knee-chest position, immediate delivery.
- Preeclampsia: hypertension after 20 weeks plus proteinuria or end-organ features. Severe features include BP ≥160/110, platelets <100, transaminases more than twice normal, creatinine >1.1 mg/dL, pulmonary oedema, and visual or cerebral symptoms. Treatment is magnesium sulfate for seizure prophylaxis, antihypertensives (labetalol, hydralazine, nifedipine) and delivery.
- Postpartum haemorrhage: tone, trauma, tissue, thrombin; give oxytocin, then tranexamic acid, then further uterotonics and balloon tamponade.
- Ectopic pregnancy: risk factors include previous ectopic, pelvic inflammatory disease and intrauterine device; an unstable patient with a positive pregnancy test goes to theatre, not to ultrasound.
Worked example
A 32-week primigravida has BP 162/108, headache and visual flashes. Platelets 90, AST 120, creatinine 1.0, urine protein 3+. This is preeclampsia with severe features. She receives magnesium sulfate, intravenous labetalol or hydralazine for blood pressure control, antenatal corticosteroids for fetal lung maturity where appropriate, and delivery is planned after stabilisation at or beyond 34 weeks. Magnesium is for seizure prophylaxis, not blood pressure control.
Traps
- Using magnesium sulfate as an antihypertensive.
- Missing ectopic pregnancy because of a single low beta-hCG.
- Forgetting that preeclampsia can occur without proteinuria when end-organ features are present.
- Delaying delivery in eclampsia for steroid benefit.