Postpartum hemorrhage

Postpartum hemorrhage means losing too much blood after giving birth. During delivery, the body has to keep bleeding in check, and it does so mainly through contractions of the uterus, the organ where the baby grew, and through the coagulation cascade, the chain of reactions in the blood that forms clots.

Here's what happens inside. When the placenta, the organ that fed the baby inside the uterus, comes out, it leaves the spiral arteries torn open. These are blood vessels that have no muscle of their own to close themselves off. They depend on the myometrium, the muscle of the uterus. Picture several open garden hoses running between the fingers of a hand: when the hand clenches tight, it squeezes them and the water stops; when the hand stays loose, the water keeps flowing. That's uterine atony: the uterus doesn't contract, and those arteries keep bleeding.

Atony is the most common cause, but it isn't the only one. The causes are summed up as the 4 Ts. Tone, when the uterus stays slack. Trauma, when there are lacerations, meaning tissues that tear during delivery. Tissue, when the placenta doesn't come out completely and part of it stays inside, which is called a retained placenta. And thrombin, the name of a key player in clotting, when the blood doesn't clot well.