What causes postpartum hemorrhage?
Once a baby is delivered, the uterus normally continues to contract (tightening of uterine muscles) and expels the placenta. After the placenta is delivered, these contractions help compress the bleeding vessels in the area where the placenta was attached. If the uterus does not contract strongly enough, called uterine atony, these blood vessels bleed freely and hemorrhage occurs. This is the most common cause of postpartum hemorrhage. If small pieces of the placenta remain attached, bleeding is also likely. It is estimated that as much as 600 ml (more than a quart) of blood flows through the placenta each minute in a full-term pregnancy.
Some women are at greater risk for postpartum hemorrhage than others. Conditions that may increase the risk for postpartum hemorrhage include the following:
Postpartum hemorrhage may also be due to other factors including the following:
Although an uncommon event (one in 2,000 deliveries), uterine rupture can be life threatening for the mother. Conditions that may increase the risk of uterine rupture include surgery to remove fibroid (benign) tumors and a prior cesarean scar in the upper part (fundus) of the uterus. It can also occur before delivery and place the fetus at risk as well.