Human triploidy: relationship between parental origin of the additional haploid complement and development of partial hydatidiform mole.

One hundred and six triploids were ascertained during a study of 1500 consecutive spontaneous abortions. The mechanism of origin of the additional haploid complement was investigated by comparing parental and foetal cytogenetic heteromorphisms and a histopathological examination of each triploid was done in a subsequent blind study. The mechanism of origin of the additional haploid complement was found to be highly correlated with the development of partial hydatidiform mole and with gestational age. All 51 paternally derived triploids in which a pathologic diagnosis could be made were partial moles, whereas only 3 of 15 maternally derived triploids on which a diagnosis could be made were molar. The mean gestational age of the paternally derived triploids was 122 days while that of the maternally derived triploids was only 74 days. It was suggested that the development of partial mole was primarily associated with the presence of two paternal haploid chromosome complements, the association with relatively long gestational ages being a secondary one consequent upon retention of the molar placentae for many weeks after foetal demise.