A 32-year-old primigravida at 28 weeks gestation presents with painless vaginal bleeding. Ultrasound confirms placenta previa. Which clinical feature best distinguishes placenta previa from placental abruption?

Explanation

## Distinguishing Placenta Previa from Placental Abruption ### Key Differentiating Features **Key Point:** Painless vaginal bleeding is the hallmark of placenta previa, whereas placental abruption typically presents with painful bleeding and uterine tenderness. ### Comparative Table | Feature | Placenta Previa | Placental Abruption | |---------|-----------------|--------------------| | **Bleeding character** | Painless, bright red | Painful, dark blood | | **Uterine tenderness** | Absent | Present (often severe) | | **Fetal distress** | Late (if at all) | Early and common | | **Maternal shock** | Proportional to visible loss | Disproportionate to visible loss | | **Ultrasound findings** | Placenta covers OS | Retroplacental clot | | **Associated HTN** | No | Yes (in 50% of cases) | ### Clinical Pearls **Clinical Pearl:** In placenta previa, the bleeding is *external* (into the vagina) and therefore visible; in abruption, bleeding is *concealed* (into the uterine cavity), making maternal shock disproportionately severe relative to visible blood loss. **High-Yield:** The **absence of pain** with **visible vaginal bleeding** is the single most reliable bedside discriminator for placenta previa. This feature is so characteristic that its presence should immediately raise suspicion for previa and prompt ultrasound confirmation. **Warning:** Do not confuse the two conditions. A patient with placenta previa who suddenly develops severe pain and shock should raise concern for *superimposed* abruption (rare but catastrophic). ### Why Other Features Are Not Discriminatory - **Elevated AFP:** Not specific to either condition; can be elevated in both or neither depending on other factors. - **Fetal heart rate abnormalities:** While more common in abruption, they can occur in severe previa with massive hemorrhage and maternal shock. - **Maternal hypertension:** A risk factor for abruption, not previa. Previa is associated with multiparity, prior cesarean, IVF, and placental abnormalities—not HTN. [cite:Williams Obstetrics 26e Ch 34]