Uterine inversion is a rare complication of childbirth that's very serious and can be life threatening. What happens is the uterus turns inside out. This can be dangerous because the mother can hemorrhage and experience quite a bit of bleeding. And it can be difficult to get the uterus back into its normal position, especially if the cervix closes around the uterus while it's inside out. On top of that, the uterus turning out can drop the mother's blood pressure to a dangerous level.
Some things that could cause a uterine inversion are the doctor pulling on the umbilical cord too hard when she's delivering the placenta, or the placenta not separating from the uterus completely. If a woman has a uterine inversion, sometimes the doctor can turn it by reaching through the vagina and pushing it. But sometimes it needs to be reversed using a surgical procedure.