"Numerous authors have looked at the role of chromosomal abnormalities in these embryonic losses. One study looked at 144 spontaneous miscarriages by obtaining direct preperations of chorionic villi. Seventy per cent had abnormal chromosomes of which 64% were autosomal trisomies, 9% polyploidy, 7% monosomy X ad 6% structural rearrangements. Errors of gonadogenesis during meiosis will result in autosomal trisomies. Errors of fertilization can result in triploidy from dispermy. Errors of the first division of the zygote result result in tetraploidy or mosaicism. None of these would be expected to be a repetitive event except in the very rare instances of balances translocations or inversions in one parent"