Parental and meiotic origin of triploidy in the embryonic and fetal periods.

Triploidy is a common finding both in early spontaneous abortions and in the fetal period. Previous studies suggested that the majority of triploidy was the result of diandry, specifically dispermy. Molecular determination of parental origin in fetal triploids has shown that digyny accounts for the majority of triploids in the fetal period. The aim of this study was to determine the meiotic level at which the error leading to digynic triploidy occurs and to extend the molecular analysis of parental origin of triploidy into the embryonic period. Maternal age of digynic triploids was compared with that of the diandric cases. Using polymorphic pericentromeric markers, we have shown that the majority of digynic triploidy is the result of errors in the second meiotic division. Digyny accounted for the majority of triploids, even in the nonfetal cases. Diandry predominated in a subset of the non-fetal cases in which embryos were not present and in which the placental findings of partial hydatidiform mole (PHM) were encountered. Maternal age differed between the digynic and diandric groups only for the non-fetal cases; this was attributed to differences in ascertainment.