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Placenta previa — USMLE Step 2 CK MCQ

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HardObstetrics & GynecologyPlacenta previaUSMLE Step 2 CK

A 32-year-old at 31 weeks of pregnancy has a first episode of painless bright-red vaginal bleeding. Maternal vital signs and fetal monitoring are reassuring. Transabdominal ultrasonography suggests a posterior low-lying placenta, but the relationship of its edge to the internal cervical os is unclear. What is the best next diagnostic step?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Perform transvaginal ultrasonography to measure the placental edge-to-os distance

Explanation lettering: D = shown as A · C = shown as B · E = shown as C · B = shown as D · A = shown as E

A is correct: transvaginal ultrasonography is safe in suspected placenta previa and more accurately defines the placental edge relative to the internal os than a limited transabdominal study. B can provoke catastrophic hemorrhage and must be avoided until previa is excluded. C is not the next test for routine placental localization. D is contraindicated and diagnostically irrelevant during an ongoing pregnancy. E does not localize the placenta or address the most likely maternal source of painless third-trimester bleeding.

Reference: ACOG Obstetric Care Consensus: placenta accreta spectrum. https://www.acog.org/clinical/clinical-guidance/obstetric-care-consensus/articles/2018/12/placenta-accreta-spectrum