Obstetrics and gynaecology for USMLE Step 2 CK

A 27-year-old woman at 32 weeks' gestation presents with painless bright red vaginal bleeding. The uterus is soft and non-tender, fetal heart tracing is reassuring, and she is hemodynamically stable. What is the most appropriate next step?

1. Transabdominal ultrasound to locate the placenta correct Correct. Painless bright red bleeding in the third trimester is placenta previa until imaging says otherwise, and ultrasound must precede any vaginal examination.
2. Administer misoprostol to induce labor Wrong and dangerous. Inducing labor in possible previa risks massive hemorrhage, and there is no indication to deliver a stable 32-week pregnancy.
3. Kleihauer–Betke test and observation alone Has a role in assessing fetomaternal hemorrhage and Rh immune globulin dosing, but it does not tell you where the placenta is.
4. Immediate cesarean delivery Premature. She is stable at 32 weeks with a reassuring tracing; expectant management with steroids is preferable to delivering a preterm infant without indication.
5. Digital vaginal examination to assess cervical dilation The classic harmful answer. Digital examination in undiagnosed placenta previa can provoke catastrophic hemorrhage.

The point: Third-trimester bleeding: painless and bright red suggests previa (ultrasound first, no digital exam); painful with a rigid tender uterus suggests abruption (clinical diagnosis, ultrasound may be normal). Give Rh immune globulin if the mother is Rh negative.

Source: ACOG practice guidance — placenta previa and third-trimester bleeding ACOG · tier 2, specialty society or college