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GBS screening — USMLE Step 3 MCQ

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HardOB/GYN (Prenatal / Contraception / Screening)GBS screeningUSMLE Step 3

At 22 weeks, an asymptomatic pregnant woman has a clean-catch urine culture growing group B Streptococcus at 30,000 CFU/mL. Repeat urinalysis shows no pyuria. She has no drug allergy. Which plan is most appropriate?

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Correct answer: A — Withhold antepartum antibiotics and plan intrapartum prophylaxis without repeat screening

The best answer is “Withhold antepartum antibiotics and plan intrapartum prophylaxis without repeat screening”. Asymptomatic GBS bacteriuria below 100,000 CFU/mL does not require antepartum treatment, but any GBS bacteriuria during pregnancy marks heavy colonization and is an indication for intrapartum prophylaxis. A later screening culture is unnecessary for that decision.

Reference: ACOG Committee Opinion: Prevention of Group B Streptococcal Early-Onset Disease: https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2020/02/prevention-of-group-b-streptococcal-early-onset-disease-in-newborns