What is hydatidiform mole and its causes? Hydatidiform mole is a gynecological disease, which is a sac tumor formed due to abnormal development of fertilized eggs. It fails to form the placenta due to abnormal development of the embryonic body, placental abnormalities occur during pregnancy, and the fetus cannot develop normally during delivery. Hydatidiform mole is caused by abnormal chromosome division after fertilization of the sperm and egg, mainly due to the sperm carrying one or two extra chromosomes. In addition, some moles are due to malformation of the embryonic body and fertilization