Chromosomal Analysis of Embryos Derived from In Vitro Fertilization of Oocytes from Old and Young Female Mice

Chromosomal abnormalities were evaluated in mouse embryos derived from in vitro fertilization using oocytes from old (12 months) BALB/c (12-BALB) and ICR (12-ICR) females and young (3 months; 3-BALB and 3-ICR) female mice. Chromosomal analysis was carried out at two developmental stages, 12-BALB and 12-ICR vs 3-BALB and 3-ICR at the first cleavage division and 12-BALB vs 3-ICR at the second division. Although all young females ovulated, this was not so in the old females; additionally, significantly fewer oocytes were ovulated by the old females and the fertilization rate was significantly lower in the 12-ICR group, but not in the 12-BALB group. Significantly fewer of the embryos in the old group had a metaphase figure at the first cleavage division and this correlated with significantly more of the embryos in this group being still at the pronuclear stage. The incidence of polyploidy, probably due to polyspermy, was found in both the 12-BALB and 12-ICR groups at the first cleavage division, but this was not seen in embryos at the second division. These results indicate that the aging of females impairs reproductive success, as evidenced by anovulation, polyspermy, and delays in fertilization/asynchronous development in resulting embryos.