To confirm and monitor pregnancy or to diagnose trophoblastic disease or germ cell tumors. Gestational trophoblastic disease (GTD) refers to a group of abnormalities in which tumors grow inside a woman's uterus (womb). The abnormal cells start in the tissue that would normally become the placenta, the organ that develops during pregnancy to feed the fetus. Ovarian germ cell tumor is a disease in which malignant (cancer) cells form in the germ (egg) cells of the ovary.