Hyperreactio luteinalis

Theca lutein cysts are benign, functional cysts of pregnancy. They are usually multiple, bilateral, and large. The exact etiology is unknown but is associated with high circulating levels of (or an increased sensitivity to) human chorionic gonadotropin (hCG), the “hormone of pregnancy.” They are typically seen in patients with trophoblastic disease, with multiple pregnancy, or who have undergone infertility treatment (ovarian stimulation followed by pregnancy). Up to 50% of patients with molar pregnancies and 10% of patients with choriocarcinoma develop theca lutein cysts. Occasionally, theca lutein cysts can occur in pregnancies associated with large placentas, such as those affected with diabetes or Rh sensitization. Rarely, they can also occur in normal, singleton pregnancies.