Malformations and anomalies

Abnormally developed blastocysts may lead to pathological proliferation of the trophoblast, which results in hydatidiform mole (mola hydatidosa). The chorionic villi accumulate a massive quantity of fluid. In most cases, there is no embryo present. The hydatidiform mole takes two forms: complete, involving all villi; partial, when major parts of the placenta appear normal. The complete hydatidiform mole does not possess chorionic vessels. The chromosome set is mostly diploid and paternal. In partial hydatidiform mole, the chromosome set is usually triploid.
While the hydatidiform mole is thought to be benign, chorionepithelioma (choriocarcinoma) is malignant. It is composed of the two parts of the trophoblast, i.e. cytotrophoblast and syncytiotrophoblast. Villi are missing. This type of tumour develops in half of the cases of complete hydatidiform mole.