Aneuploidy in human preimplantation embryos

Even when conditions are optimal, the chance of a clinically recognized pregnancy occurring in a given menstrual cycle is much less than half. Besides failure of conception pre-clinical pregnancy loss is a major cause for the low fecundity observed in humans. Chromosome abnormalities are the predominant cause of this clinical problem, both in natural conceptions as well as after assisted reproduction [21]. About 42 % of all oocytes exposed to natural fertilization survive until after implantation, and only 31 % will lead to a live birth (Fig. 17.1)