Complete moles, or molar pregnancies, are a type of gestational trophoblastic disease where abnormal tissue grows inside the uterus instead of a normal embryo. This condition occurs when an egg is fertilized by a sperm, but instead of developing into a fetus, the tissue forms a mass of cysts. There are two types of complete moles: complete hydatidiform moles and partial moles. In a complete mole, there is no normal fetal tissue, while a partial mole may contain some normal tissue but is still mostly abnormal. Symptoms can include abnormal bleeding and an enlarged uterus.