Placenta Previa
Painless, bright red vaginal bleeding in the third trimester should trigger one absolute rule: nothing enters the vagina until an ultrasound confirms placental location.
Core Concept
Placenta previa occurs when the placenta implants over or near the internal cervical os. It is classified as complete (fully covers the os), partial, marginal, or low-lying. The hallmark presentation is painless, bright red vaginal bleeding — typically appearing after 28 weeks when the lower uterine segment thins and stretches, disrupting placental attachment. The bleeding is episodic, often starts without provocation, and may worsen with each episode. Diagnosis is confirmed by ultrasound; transvaginal ultrasound is the gold standard and is safe when performed by a trained provider, but digital cervical exams are absolutely contraindicated because even gentle manipulation can trigger catastrophic hemorrhage. Risk factors include prior cesarean birth, multiparity, advanced maternal age, smoking, and prior previa. A complete previa mandates cesarean delivery. Marginal or low-lying placenta identified early may resolve as the uterus grows (placental migration), so a follow-up ultrasound around 32–36 weeks determines delivery planning. Nursing priorities include pelvic rest (no intercourse, no tampons), bed rest, continuous FHR monitoring, IV access, type and crossmatch, Rh status assessment with RhoGAM if Rh-negative, and no vaginal exams.
Watch Out For
Don't confuse placenta previa (painless, bright red bleeding, soft nontender uterus) with placental abruption (painful, dark red bleeding, rigid board-like uterus). Students mix up the two because both cause third-trimester bleeding, but the physical exam findings are opposite. Also remember: previa bleeding is external and visible, while abruption can be concealed with no visible bleeding at all.
Clinical Pearl
Painless = previa, painful = abruption. If bleeding is bright red and the uterus is soft, think previa — and keep your hands out until ultrasound says otherwise.
Test Your Knowledge
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