## **Core Concept**
Postpartum hemorrhage (PPH) is a leading cause of maternal morbidity and mortality worldwide. It is defined as excessive bleeding following delivery, typically exceeding 500 mL after vaginal delivery or 1000 mL after cesarean section. The causes of PPH can be categorized into four main areas: uterine atony, lacerations, retained placental tissue, and coagulopathy.

## **Why the Correct Answer is Right**
The correct answer, uterine atony, is the most common cause of PPH, accounting for approximately 70-80% of cases. Uterine atony refers to the failure of the uterus to contract down effectively after delivery, leading to excessive bleeding from the placental site. This condition can occur due to various factors, including prolonged labor, overdistension of the uterus (as in multiple gestations or polyhydramnios), and the use of certain medications like magnesium sulfate.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Lacerations, although a significant cause of PPH, are less common than uterine atony. They can occur during delivery and may not always be immediately apparent.
- **Option C:** Retained placental tissue can cause PPH but is less frequent than uterine atony. It often requires manual removal or surgical intervention.
- **Option D:** Coagulopathy is a less common cause of PPH but can be severe and life-threatening. It may result from pre-existing conditions, severe hemorrhage, or amniotic fluid embolism.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that early recognition and management of uterine atony are crucial to prevent severe PPH. The "Four Ts" are often remembered: **Tone** (uterine atony), **Trauma** (lacerations), **Tissue** (retained placental tissue), and **Thrombin** (coagulopathy). Uterine massage, administration of uterotonic agents like oxytocin, and surgical interventions are mainstays of treatment.

## **Correct Answer:** . Uterine Atony