Also known as premature separation of the placenta or placental abruption, the partial or complete separation of the placenta from the uterus before delivery of the fetus. It occurs in less than 2% of pregnancies. When severe, in 1:500-750 deliveries, fetal death may result (50% of cases).

Separation is initiated by hemorrhage into and delamination of the decidua basalis with subsequent separation of the adjacent placenta and blood clot formation between the placenta and uterine wall (Figure 13-1). In most cases the bleeding progresses to the placental edge. Usually, initial hemorrhage is encountered after the 26th week of gestation. In early pregnancy, placental separation cannot be differentiated from other causes of abortion. Fifty percent of premature separations occur before labor begins; 10-15% are not diagnoses before the second stage of labor.

In the concealed form (20%) hemorrhage is confined to the uterine cavity; it may break through the extraplacental membranes and enter the amniotic cavity. Placental detachment may be complete and complications are often severe. Five to eight percent develop coagulopathies with increased risk for fetal demise.

In the external/apparent form (80%) blood tracks down between the chorion and decidua vera and drains through the cervix. Placental detachment is more commonly incomplete, and there are fewer and less severe complications. It may involve the placental margin.

In the relatively concealed form hemorrhage from a partially detached placenta is concealed by intact extraplacental membranes.

Placental abruption

Etiology. Predisposing factors include: 1) previous placental separation (with 1 prior abruption the incidence of recurrence is 10-17%; with 2, the incidence of recurrence is greater than 20%); 2) hypertensive states of pregnancy increase the risk for premature placental separation by 2-8% (abruption severe enough to cause fetal death is associated with hypertensive states of pregnancy in 50% of cases; half have chronic hypertension, while the other half have pregnancy induced hypertension); 3) advanced maternal age; 4) multiparity; 5) uterine distention (multifetal gestation, polyhydramnios); 6) vascular deficiency or deterioration (diabetes mellitus, collagen vascular disease); 7) uterine tumors or anomalies (fibroids); 8) cigarette smoking; 9) consumption of more than 14 alcoholic drinks per week; 10) cocaine use.

Etiology. Precipitating factors include (all rare): 1) circumvallate placenta; 2) trauma (external or internal version, motor vehicle accident, abdominal trauma carried to an anteriorly implanted placenta); 3) sudden reduction in uterine volume (rapid loss of amniotic fluid, delivery of first twin); 4) traction on an abnormally short umbilical cord (a problem more common during delivery); 5) increased venous pressure, particularly when abrupt or extreme.

Risk. Thirty percent of abruptions are small, produce few or no symptoms and usually are not noted until placental examination. Twenty percent of cases will be incorrectly diagnosed as idiopathic preterm labor. Fetal mortality is high (50-80%). In 15% of cases there are no fetal heart tones at labor. In 50%, fetal distress due to decreased metabolic exchange from decreased placental surface, maternal hemorrhage with decreased uterine perfusion and fetal hemorrhage, is noted early. Live born infants have a high rate of morbidity due to prenatal hypoxia, birth trauma and the consequences of prematurity (40-50%). There is a risk for uterine apoplexy/Couvelaire uterus.

Worldwide, maternal mortality (0.5-5%) is usually due to immediate or delayed hemorrhage, or cardiac or renal failure. A high degree of clinical suspicion, followed by early diagnosis and definitive therapy should reduce the maternal mortality rate to 0.5-1.0%.