Molar pregnancy is a rare complication of pregnancy in which trophoblastic tissue (which in a standard pregnancy forms the placenta) proliferates abnormally.
Molar pregnancy is a disease of benign behavior in most cases, but it can give rise to gestational trophoblastic neoplasia which has malignant features.
The most common form of molar pregnancy is hydatidiform mole, which can be complete or partial. In the complete form there is only abnormal placental tissue and in the partial form there is also fetal tissue. Partial hydatidiform mole has a benign behavior most of the time and only becomes malignant in 4% of cases, while complete hydatidiform mole is malignant in up to 20% of cases. After the treatment of molar pregnancy, a strict follow-up with frequent controls should be followed for a long period of time, because in some cases the disease can persist and give rise to gestational trophoblastic neoplasia, which can have different degrees of malignancy and give rise to tumors.