Obstetrics: Normal Pregnancy and Prenatal Care
What this domain tests
Normal pregnancy items check whether you can date a pregnancy accurately, apply a risk-based prenatal schedule, and interpret routine screening without over-testing. The Iranian national prenatal guideline anchors these answers: early booking, a documented estimated date of delivery (EDD), supplementation, and scheduled ultrasound and glucose screening.
Core rules
- Dating. Crown–rump length at 7–13+6 weeks is the most accurate method (±5–7 days). Naegele's rule: first day of LMP + 280 days (+1 year, −3 months, +7 days). If a first-trimester scan differs from LMP by more than 5–7 days, the scan wins.
- Gravidity/parity. Gravida counts every pregnancy including the current one; para counts births at ≥20 weeks (or ≥500 g), not pregnancies. TPAL removes ambiguity.
- Supplementation. Folic acid 400 µg daily from at least 1 month before conception through the first trimester; 5 mg for prior neural tube defect, pregestational diabetes, obesity, or valproate use. Elemental iron 60 mg daily from about week 16 is standard in Iran.
- Schedule. Visits every 4 weeks to 28 weeks, every 2 weeks to 36, then weekly. Fundal height from 24 weeks should track within 2–3 cm of gestational age.
- Screening. Combined first-trimester screening at 11–13+6; anomaly scan at 18–22 weeks; 75-g 2-hour OGTT at 24–28 weeks with thresholds 92/180/153 mg/dL. Give Td and influenza vaccine as indicated; live vaccines are contraindicated.
Worked example
A woman books with uncertain LMP. A scan on 10 March gives a CRL consistent with 8 weeks 4 days (60 days). EDD = scan date + (280 − 60) = 10 March + 220 days ≈ 16 October. Because the scan is before 14 weeks, it overrides any LMP-based date.
Traps that cost marks
Calling a woman gravida 1 because she has one living child; redating a 30-week pregnancy for a 10-day scan discrepancy; treating a 50-g glucose challenge result as diagnostic; giving MMR in pregnancy.