Polyploidy in mouse embryos derived from in vivo and in vitro fertilization is dependent on the timing of pregnant mare serum gonadotropin (PMSG) injection.

Nine hundred eighty-seven mouse embryos were cytogenetically analyzed at the two-cell stage to compare aneuploidy rates in embryos derived from both in vivo and in vitro fertilization using two different ovarian stimulation protocols. The rate of polyploidy was significantly (P<.001) elevated in both in vivo fertilized (15.6%) and in vitro fertilized (5.9%) embryos when PMSG injection was given in the afternoon instead of the morning (2.1% and 4.0% respectively).