Hyperreactio luteinalis associated with severe twin-to-twin transfusion syndrome.

Twin-to-twin transfusion syndrome (TTTS) is a severe complication of monochorionic twin pregnancies, with high perinatal loss and significant morbidity. The etiology of this syndrome remains unclear. Hyperreactio luteinalis is a rare benign condition characterized by maternal ovarian enlargement due to theca lutein cysts. We present 4 cases of hyperreactio luteinalis associated with severe TTTS. We detected maternal ovarian enlargement by prenatal ultrasonography in 2 cases, at the cesarean section in 1 case, and postpartum in 1 case. Three cases showed hydrops fetalis and all cases showed congestive cardiac failure. Serial amnioreduction was performed in all cases, and regression of hydrops fetalis and maternal ovarian enlargement occurred in 1 case. These cases suggest that the pathophysiology of TTTS is closely related to the etiology of hyperreactio luteinalis.