Hydatidiform moles.
This gestational neoplasm arises from the trophoblast, the ectodermal layer of a fertilized ovum. Although benign, hydatidiform moles have the potential to progress to malignant trophoblastic disease. Molar pregnancy must be recognized promptly. The clinical presentation is usually vaginal bleeding, which may contain characteristic tissues. Diagnosis is confirmed by identification of hydropic avascular villi obtained by evacuation of uterine contents. The beta subunit of human chorionic gonadotropin is a valuable tumor marker.