These are benign, functional cysts which result from enlargement of an otherwise normal follicle known to be present during the third trimester and early neonatal period 3,4,5 . Evidence suggests that ovarian cysts result from excessive stimulation of the fetal ovary by placental and maternal hormones. It has been observed that there was slightly higher prevalence of ovarian cysts in the fetuses when the pregnancy was complicated by diabetes, pre-eclampsia, or rhesus immunization, presumably associated with excessive release of placental chorionic gonadotrophins by the enlarged placenta. Fetal hypothyroidism has also been associated with ovarian cysts, and the nonspecific stimulation of pituitary glycoprotein hormone synthesis has been thought to be a cause for the ovarian cyst 6,7 . Pathology Unilateral cysts are more common than bilateral, and unilocular cysts, are more common than multilocular cysts.
Size varies and ranges from small cysts to structures filling the entire abdomen.
Granuloma cell tumors, benign cystic teratomas, and mesonephromas have been reported in newborns, but they are rare compared to the cysts of germinal origin 8,9 . Fetal ovarian cysts are the most common cause of intra-abdominal cysts reported antenatally, excluding renal and bowel etiologies. An ovarian cyst should be suspected when a female fetus has a cystic intra-abdominal mass which is separate from the organs of the urinary and gastrointestinal tract. Ovarian cysts frequently have been diagnosed on prenatal sonography 10-16 . In no case has a fetal ovarian cyst been reported before the third trimester.