Diploid hydatidiform moles with fetal red blood cells in molar villi. 2--Genetics.

The purpose of this study was to determine the genetic origin of a series of seven diploid hydatidiform moles with fetal red blood cells in the molar villi, normally a characteristic feature of triploid, partial hydatidiform moles. DNA was prepared from formalin-fixed, paraffin-embedded blocks of molar tissue and blood from the patient and her partner. The genetic origin of molar tissue was determined by comparing microsatellite polymorphisms in molar and parental tissue following polymerase chain reaction (PCR) amplification of DNA. In six cases, the hydatidiform mole was shown to be androgenetic in origin and therefore genetically to be a complete hydatidiform mole. In one case, the hydatidiform mole was of biparental origin, having both a maternal and a paternal contribution to the genome. We conclude that fetal red blood cells may be observed in the villi of complete hydatidiform moles. In cases where the degree of trophoblastic hyperplasia and ploidy is suggestive of a complete hydatidiform mole, the presence of fetal red blood cells alone should not be considered indicative of a diagnosis of partial hydatidiform mole.