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. Placental detachment may be complete and complications are often severe. Five to eight percent develop coagulopathies with increased risk for fetal demise.
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. 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.