The influence of strain, maternal age, and method of maturation on mouse oocyte aneuploidy.

The chromosome complement of metaphase II oocytes matured by different methods was determined. These oocytes were collected from young and old Swiss-Webster random bred and CBA inbred mice. The results from the two strains were remarkably similar. Superovulation caused no increase in aneuploidy frequencies; however, in vitro maturation resulted in increased hyperploidy rates for oocytes from younger females of both strains. Of the six possible comparisons regarding a maternal age effect, there were no significant increases in hyperploidy. The absence of a maternal age effect on the first meiotic division of oocytes, while such an effect does exist for mid-gestation mouse fetuses, suggests that the maternal age effect on aneuploidy may be due to a decreased ability to select against (abort) aneuploid embryos/fetuses as a function of increasing maternal age.