Origin of triploidy in spontaneous abortuses

Fourteen triploid spontaneous abortuses were studied cytogenetically by sequential Q and C banding and the marker chromosomes were compared with those of the parents. The abortuses comprised all triploid cases in a series of 288 consecutive abortuses of the first 16 weeks of pregnancy occurring in one hospital. In 12 of the triploids the origin of the extra haploid set was conclusively determined, revealing six cases of dispermy, five failures in the first maternal and one failure in the first paternal meiotic division. The results were combined with those of five other studies comprising a total of 48 informative cases. Non-reduction in the second meiotic division seems to be of little or no significance in the origin of human triploidy. Dispermy is the predominant source, accounting for 40--50% of the triploid spontaneous abortuses. Non-reduction in the first meiotic division of the father seems to be the second-most frequent source although in the present material the corresponding maternal non-reduction is much more common.