It is frequently difficult to determine the exact causes of placenta abruptio. Definable, direct causes that result in placenta abruptio are quite rare (1 to 5%). They include mechanical factors such as abdominal trauma (for example, from an auto accident or fall), sudden loss in uterine volume as occurs with rapid loss of amniotic fluid or the delivery of a first twin, or an abnormally short umbilical cord (usually only a problem at the time of delivery).
Risk factors include the following: - A placenta abruptio in a previous pregnancy. After one prior episode there is a 10 to 17% recurrence; after two previous episodes the chance of recurrence exceeds 20%.
- High blood pressure during pregnancy is associated with a placenta abruptio rate of 2.5 to 17.9%. This may be caused by pre-eclampsia, eclampsia, or other conditions. Approximately 50% of placenta abruptio cases severe enough to cause fetal death are associated with hypertension.
Other risk factors include increased maternal age; increased number of prior deliveries; increased uterine distention (as may occur with multiple pregnancies or abnormally large volume of amniotic fluid); diabetes in the pregnant woman; cigarette smoking; cocaine abuse; and drinking more than 14 alcoholic drinks per week during pregnancy.
The incidence of placenta abruptio, including any amount of placental separation prior to delivery, is about 1 out of 150 deliveries. The severe form, which results in fetal death, occurs only in about 1 out of 500 to 750 deliveries.
| 
