Partial moles: from postnatal to prenatal diagnosis.

The partial hydatidiform mole is a histopathologic entity characterized by focal trophoblastic hyperplasia with villous hydrops together with identifiable fetal tissue which was first described by Szulman and Surti in 1978. Since then major advances in molecular biology have shown that more than 90 per cent of partial moles are secondary to diandric triploidy and that this condition accounts for most cases of persistent trophoblastic disease after partial mole. Case series describing the prenatal diagnosis of triploid partial mole were reviewed and outcomes were analysed for all pregnancies, and compared to those of non-molar triploidy using the chi-square test. In more than 90 per cent of both types of triploidy, the fetus shows growth restriction and multiple structural anomalies. Oligohydramnios and abnormal placental Doppler indices are common in both types. In triploid partial mole, 82.1 per cent of fetuses present with symmetrical growth restriction, the maternal serum human chorionic gonadotropin (MShCG) level is increased in 80.8 per cent of the cases and 41.9 per cent of the women are at risk of pre-eclampsia. The triploid partial mole is a lethal fetal condition which is linked with gestational trophoblastic disorders. The typical placental molar features are not always pathognomonic of triploid partial mole and are less likely to be apparent on ultrasound in early pregnancy. The perinatal diagnosis of this condition relies upon mainly on MShCG level and cytogenetic results which have to be correlated with the histopathologic diagnosis. Women with this pregnancy complication should be offered immediate termination and a specific follow-up.