A 28-year-old primigravida at 39 weeks gestation presents with vaginal bleeding and abdominal pain. On examination, the uterus is tender and contracting. Cardiotocography shows fetal bradycardia. Which feature best distinguishes placental abruption from placenta previa as the indication for emergency cesarean section?

Explanation

## Distinguishing Placental Abruption from Placenta Previa ### Key Clinical Discriminator **Key Point:** Uterine tenderness and evidence of maternal hypovolemic shock are hallmark features of placental abruption, distinguishing it from placenta previa. ### Comparative Table | Feature | Placental Abruption | Placenta Previa | |---------|-------------------|------------------| | **Uterine tenderness** | Present (prominent) | Absent | | **Maternal shock** | Common (concealed bleeding) | Rare (visible bleeding) | | **Vaginal bleeding** | May be concealed (retroplacental) | Always visible | | **Fetal distress** | Common (due to placental insufficiency) | Variable | | **Uterine contractions** | Present, often tetanic | Absent (relaxed uterus) | | **Coagulopathy** | Frequent (DIC) | Absent | ### Clinical Pearl **Clinical Pearl:** In placental abruption, the bleeding is often *concealed* behind the placenta, leading to a discrepancy between visible vaginal bleeding and degree of maternal shock. Uterine tenderness reflects the retroplacental hematoma and irritation of the myometrium. In contrast, placenta previa presents with *visible* vaginal bleeding without uterine tenderness or shock (unless massive hemorrhage occurs). ### High-Yield Distinction **High-Yield:** The **tetanic uterus + tenderness + shock** triad is pathognomonic for abruption and mandates emergency cesarean delivery. Placenta previa typically presents with painless vaginal bleeding and a soft, relaxed uterus. ### Pathophysiology In abruption, the placenta separates prematurely from the decidua, causing: 1. Retroplacental hematoma formation → uterine irritation and tenderness 2. Concealed hemorrhage → maternal hypovolemia and shock disproportionate to visible bleeding 3. Release of thromboplastin → consumptive coagulopathy (DIC) 4. Placental insufficiency → fetal hypoxia and distress In previa, the placenta is abnormally implanted over the cervical os but remains attached; bleeding is from exposed placental vessels at the cervix and is visible.