## **Core Concept**
Postpartum hemorrhage (PPH) is a leading cause of maternal morbidity and mortality worldwide. It is defined as excessive bleeding following the birth of a baby, typically considered to be more than 500 mL after vaginal delivery or more than 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**
Uterine atony is the most common cause of PPH, accounting for approximately 70-80% of cases. It occurs when the uterus fails to contract down effectively after delivery, leading to excessive bleeding from the placental site. This can be due to various factors such as prolonged labor, overdistension of the uterus (as in multiple gestations or polyhydramnios), and 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 leads to bleeding because the placenta's site does not heal properly without complete removal of the placental tissue.
- **Option D:** Coagulopathy is a less common cause of PPH and can be due to pre-existing conditions or complications during pregnancy and delivery. It results in the failure of blood to clot properly.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that early recognition and management of PPH are critical to prevent severe outcomes. The "Four Ts" of PPH management are: **Tone** (assessing for uterine atony), **Trauma** (evaluating for lacerations), **Tissue** (checking for retained placental tissue), and **Thrombin** (assessing coagulation status). Uterine massage and uterotonic agents like oxytocin are first-line treatments for uterine atony.

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