Hydatidiform mole. Light micrograph of a section through tissue from the uterus, in a case of a hydatiform mole. This is an abnormal form of pregnancy, where a genetic imbalance prevents normal development of the embryo. The membrane around the embryo (the chorion) degenerates, forming a collection of fluid-filled sacs. There is a risk that cells from a hydatidiform mole may go on to form a cancer known as choriocarcinoma.