Cytogenetic effects of advanced maternal age and delayed fertilization on first-cleavage mouse embryos.

It has been shown that both advanced maternal age and delayed fertilization may induce chromosomal anomalies. We therefore examined the combined effects of these two factors on chromosomal anomalies in first-cleavage mouse embryos. We set up normal and (6-h) delayed subgroups in two different age groups (young, 3-4 mo; aged, 9-11 mo) and compared the incidence of chromosomal anomalies. In first-cleavage embryos, egg-derived chromosomes can be distinguished from sperm-derived chromosomes. The incidence of maternally derived aneuploidy was highest in the aged-delayed fertilization subgroup. We therefore conclude that advanced maternal age affects the production of aneuploidy more severely when combined with the effect of delayed fertilization.