Gestational trophoblastic disease (GTD) is a term for a group of rare tumors that form in the tissue that surrounds an egg after it is fertilized. This tissue is made of trophoblast cells, which connect the fertilized egg to the wall of the uterus and form part of the placenta. In GTD, a tumor forms instead of a healthy fetus.

The two main types of GTD are hydatidiform moles and gestational trophoblastic neoplasia. Hydatidiform moles are also called molar pregnancies and are more common. Most hydatidiform moles are benign (not cancer), but they sometimes become cancer. Gestational trophoblastic neoplasia is almost always malignant (cancer). There are different types of gestational trophoblastic neoplasia, including invasive moles, choriocarcinomas, placental-site trophoblastic tumors, and epithelioid trophoblastic tumors.

GTD may not cause early signs and symptoms and may seem to be a normal pregnancy. Later signs of GTD include abnormal vaginal bleeding and a uterus that is larger than normal. GTD is usually found early during routine pregnancy care, and most of the time can be cured.