Subchorionic hematoma: a review.

A review of the English literature on subchorionic hematoma (SCH) is presented. Fourteen studies are reviewed. The incidence of SCH varied greatly among studies from 4 to 48 per cent. Small SCH tend to be more common in the first trimester and appear to pose no added risk to the ongoing pregnancy. Conversely, SCH in the second trimester often are larger and may be associated with an increased risk of preterm delivery. The etiology of these hematomas remains unclear. Pathological changes that might contribute to their formation are reviewed. Larger studies with controls, including data on the incidence of SCH in a population of normal obstetric patients are needed.