The partial or complete separation of the placenta from the uterus can cause bleeding from the placental bed. Blood builds up and eventually escapes around the membranes and I through the cervix into the vagina. This is known as placental abruption (abruptio placentae) and happens in about one in 200 pregnancies. Causes of placental abruption include smoking (risk rises with the number of cigarettes smoked per day); uncontrolled high blood pressure; trauma; and illicit drug use. Obstetricians divide placental separation into three types according to the severity. If severe placental abruption happens before the third trimester, a baby may die, but it can survive less severe separations.

In mild separation, your blood loss may be slight. You’ll need bed rest, with ultrasound examination to monitor the situation. If it happens late in pregnancy, your labor may have to be induced.

In moderate separation, one-quarter of the placenta separates and between one and two pints (500 ml to one liter) of blood is lost. A blood transfusion is needed and, if your pregnancy is at or nearing term, you’ll usually need a cesarean section.

Severe separation is an acute emergency, when at least two­thirds of the placenta shears off the uterine wall, and up to four pints (two liters) of blood are lost. This causes severe shock, disturbance of blood coagulation, and full kidney shutdown. A rapid blood transfusion will be given, and if the pregnancy is near term, a cesarean may be carried out to try to save the baby.

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