What is the most common cause of postpartum hemorrhage?

Uterine atony is recognized as the most common cause of postpartum hemorrhage, accounting for a significant majority of cases. This condition occurs when the uterus fails to contract effectively after childbirth, leading to excessive bleeding. Normally, after delivery, the uterus should contract to compress the blood vessels that were supplying the placenta, thereby minimizing blood loss.

Several risk factors can contribute to uterine atony, including prolonged labor, multiple gestations, high parity, and the use of certain medications during labor. The failure of these contractions results in a condition known as atonic uterus, which is the primary reason for immediate postpartum hemorrhage.

While the other options can contribute to postpartum hemorrhage, they are less common in comparison to uterine atony. For instance, retained placenta involves the failure to deliver the placenta completely, which can lead to further complications but occurs less frequently than atony. Placental abruption and uterine rupture are serious but rarer conditions that can also result in significant bleeding, but they do not account for as many cases as uterine atony does. Understanding this can help in recognizing that while several factors contribute to postpartum hemorrhage, uterine atony is the predominant concern in the majority of cases.