Master Reproductive System (Obs & Gyn)
for PLAB 1

What the PLAB 1 Tests in Reproductive System (Obs & Gyn)

The PLAB 1 exam tests the management of common obstetric and gynaecological presentations in a UK primary care or emergency setting. Candidates must demonstrate knowledge of antenatal care (screening, complications like pre-eclampsia and gestational diabetes), labour and delivery (induction, fetal monitoring, postpartum haemorrhage), and gynaecological emergencies (ectopic pregnancy, miscarriage, ovarian torsion). Key decisions include when to refer, which first-line drugs to prescribe (e.g., labetalol for hypertension, misoprostol for PPH), and interpretation of investigations (e.g., hCG, ultrasound, CTG). The exam emphasises NICE and RCOG guidelines, red-flag symptoms, and safe prescribing in pregnancy.

High-Yield Concepts

• Pre-eclampsia diagnosis and management: Diagnose with BP ≥140/90 mmHg after 20 weeks plus proteinuria (≥300 mg/24h) or other end-organ dysfunction. First-line oral antihypertensive: labetalol 200 mg BD, titrate up. For severe pre-eclampsia (BP ≥160/110), give IV labetalol or oral nifedipine MR. Deliver if ≥37 weeks; before 34 weeks, give betamethasone 12 mg IM x2 doses 24h apart for fetal lung maturity.
• Gestational diabetes screening and treatment: Screen at 24-28 weeks with 75g OGTT: fasting ≥5.6 mmol/L, 2-hour ≥7.8 mmol/L. First-line: metformin 500 mg OD, titrate to max 2.5 g/day; add insulin (e.g., Humulin NPH) if targets not met (fasting <5.3, 1h postprandial <7.8). Monitor fetal growth with ultrasound every 4 weeks.
• Ectopic pregnancy management: Present with abdominal pain, amenorrhoea, adnexal mass. Diagnosis: transvaginal ultrasound showing empty uterus with adnexal mass, hCG >1500 IU/L. Stable patient with mass <35 mm, no fetal heart activity, hCG <1500: give methotrexate 50 mg/m² IM single dose. Unstable or failed medical: laparoscopic salpingectomy.
• Postpartum haemorrhage (PPH) protocol: Primary PPH: blood loss >500 mL (vaginal) or >1000 mL (CS). First-line: oxytocin 5 IU slow IV, then oxytocin infusion (40 IU in 500 mL saline over 4h). If ongoing: ergometrine 0.5 mg IM (avoid in hypertension), misoprostol 800 mcg PR, or carboprost 250 mcg IM (contraindicated in asthma). Massive transfusion protocol if haemodynamically unstable.
• CTG interpretation and fetal distress: Normal CTG: baseline 110-160 bpm, variability 5-25 bpm, accelerations present, no decelerations. Suspicious: reduced variability, late decelerations, variable decelerations >50% of contractions. Pathological: prolonged deceleration >3 min, sinusoidal pattern. Action: if suspicious, start fetal scalp electrode; if pathological, consider urgent delivery (category 1 CS within 30 min).
• Miscarriage types and management: Threatened: closed cervix, viable pregnancy on scan — no treatment, advise rest. Inevitable: open cervix, bleeding — admit. Incomplete: retained products — misoprostol 800 mcg PV (single dose) or suction evacuation. Missed: fetal demise retained — expectant (up to 14 days) or misoprostol 800 mcg PV. Recurrent (≥3 losses): refer for thrombophilia screen, karyotyping.
• Ovarian hyperstimulation syndrome (OHSS): Occurs after IVF or gonadotropin therapy. Mild: abdominal bloating, nausea — manage with fluids, analgesia. Moderate: ascites, oliguria — admit, IV fluids, monitor electrolytes. Severe: respiratory distress, tense ascites, creatinine >1.2 mg/dL — treat with paracentesis, IV albumin 25% 100 mL 6-hourly, consider ICU. Prevent with GnRH antagonist protocols.
• Induction of labour (IOL) methods: Indications: post-term (≥41 weeks), PROM, IUGR, maternal hypertension. Bishop score <6: use dinoprostone (PGE2) 10 mg pessary or 1-2 mg gel PV, repeat after 6h if needed. Bishop score ≥6: ARM followed by oxytocin infusion (start 1-2 mU/min, increase by 1-2 mU/min q30min). Contraindications: placenta praevia, transverse lie, previous classical CS.

Common Traps in Reproductive System (Obs & Gyn) Questions

• Confusing pre-eclampsia with gestational hypertension: proteinuria is required for pre-eclampsia, but severe features (e.g., thrombocytopenia, elevated LFTs) can diagnose it without proteinuria.
• Using ergometrine for PPH in a hypertensive patient: it causes vasoconstriction and can precipitate a hypertensive crisis; use oxytocin or misoprostol instead.
• Assuming a negative urine pregnancy test rules out ectopic pregnancy: urine tests can be negative if hCG is low; always check serum hCG and ultrasound.
• Treating gestational diabetes with insulin first-line in all cases: NICE recommends metformin as first-line unless contraindicated or patient prefers insulin.
• Failing to differentiate between threatened and inevitable miscarriage: a closed cervix on speculum exam is key to avoid unnecessary intervention.
• Misinterpreting a sinusoidal CTG as fetal sleep: sinusoidal pattern indicates severe fetal anaemia or hypoxia, requiring immediate delivery.

How to Revise Reproductive System (Obs & Gyn) for the PLAB 1

Focus on NICE guidelines for common obstetric emergencies (PPH, pre-eclampsia, cord prolapse) and gynaecological triage (ectopic, miscarriage, ovarian torsion). Questions often present a clinical scenario with a lab value or imaging result, then ask for the next step in management — not just diagnosis. Practise interpreting CTG traces, Bishop scores, and hCG trends. Prioritise drug doses (e.g., oxytocin, methotrexate, labetalol) and contraindications in pregnancy. Review RCOG green-top guidelines for heavy menstrual bleeding (first-line: tranexamic acid or mefenamic acid) and endometriosis (first-line: combined oral contraceptive or progestogen). Expect 2-3 questions on antenatal screening (e.g., Down's syndrome combined test at 11-14 weeks) and postnatal care (e.g., breastfeeding support, postpartum depression screening with EPDS).

Practise it: MedLumen has 40 Reproductive System (Obs & Gyn) questions for the PLAB 1, each with a full explanation and references.