The separation of the placenta from the site of uterine implantation before delivery of the fetus.

It is frequently difficult to determine the exact causes of placenta abruptio. Definable, direct causes that trigger placentaabruptio are quite rare (1 to 5%). They include mechanical factors such as abdominal trauma (for example, from an autoaccident or fall), sudden loss in uterine volume as occurs with rapid loss of amniotic fluid or the delivery of a first twin, or anabnormally short umbilical cord (usually only a problem at the time of delivery).Predisposing factors include the following risk factors: a past medical history of placenta abruptio (after 1 prior episode thereis a 10 to 17% recurrence, after 2 prior episodes the incidence of recurrence exceeds 20%); hypertension or high blood pressureduring pregnancy is associated with 2.5 to 17.9% incidence (however, approximately 50% of placenta abruptio cases severeenough to cause fetal death are associated with hypertension); increased maternal age; increased number of prior deliveries;increased uterine distention (as may occur with multiple pregnancies or abnormally large volume of amniotic fluid); diabetesmellitus in the pregnant woman; cigarette smoking; and drinking alcohol during pregnancy (more than 14 drinks per week).The incidence of placenta abruptio, including any amount of placental separation prior to delivery, is about 1 out of 77 to 89deliveries. However, the severe form (resulting in fetal death) occurs only in about 1 out of 500 to 750 deliveries.

Avoiding behavioral risk factors, early and continuous prenatal care, and early recognition and adequate management ofmaternal conditions such as diabetes mellitus and hypertension decrease the risk of placenta abruptio.