Predisposition to aneuploidy in the oocyte.

While the incidence of predisposition to aneuploidy in the oocyte increases with age, there is also evidence of increased incidence in young women with recurrent miscarriage, recurrent aneuploidy, or recurrent implantation failure after in vitro fertilization. There is evidence from mouse models and from observations in humans that follicle-stimulating hormone (FSH) probably has a direct or indirect effect on the occurrence of oocyte aneuploidy. It seems that increased endogenous or exogenous FSH could induce meiotic disruption. Although the effect of FSH may explain the age-related increase in aneuploidy rate, many questions remain regarding young women, even if their FSH level is sometimes increased. Disruption of meiotic gene expression caused by exposure to environmental contaminants or by gene defects could also predispose to oocyte aneuploidy. Such abnormalities could impact on the oocyte pool, recombination and synapsis during fetal life, or oocyte growth.