Antepartum Care and Prenatal Assessment
Antepartum Care and Prenatal Assessment
This domain tests whether you can establish gestational age, individualize prenatal screening, recognize maternal-fetal risk, and document a safe surveillance plan. Licensing items often ask for the next test or the correct interpretation, not broad recall.
Core rules
- EDD: use a reliable LMP only if cycles are regular and no conflicting ultrasound. ACOG treats first-trimester CRL (7+0 to 13+6 weeks) as most accurate; if CRL dating differs by >7 days from LMP, redate. Do not redate after 14 weeks solely for size.
- Visit cadence for uncomplicated pregnancy: every 4 weeks to 28 weeks, every 2 weeks to 36 weeks, then weekly until birth.
- Aneuploidy screening: cell-free DNA from 10 weeks; first-trimester combined screen 11+0-13+6; quad screen 15-22 weeks. Offer diagnostic testing after a positive screen.
- GDM: screen at 24-28 weeks. One-step 75-g OGTT thresholds: fasting ≥92, 1 hour ≥180, 2 hours ≥153 mg/dL.
- Preeclampsia prevention: low-dose aspirin 81 mg daily from 12-16 weeks for high-risk patients.
- RhD immunoglobulin at 28 weeks for unsensitized RhD-negative patients; Tdap at 27-36 weeks; influenza and COVID-19 vaccines as indicated.
Worked example
A patient with irregular cycles has LMP suggesting 8 weeks, but CRL at ultrasound is 6+2. The difference is 12 days, exceeding the 7-day first-trimester threshold, so the ultrasound EDD governs. Document the redating and adjust all screening windows. The reasoning: dating error changes GDM screening, preterm labor management, and post-term planning.
Traps
Using LMP in irregular cycles; redating after 14 weeks for small growth; missing the aspirin window; treating a positive screen as diagnosis without counseling about diagnostic testing.