Analysis of the chromosome complement of frozen-thawed mouse oocytes after parthenogenetic activation.

Frozen-thawed mouse oocytes were artificially activated with Sr2+ and analyzed cytogenetically at the first cleavage division to examine the behavior of the maternal chromosomes independently of the paternal complement. There was no significant difference in the rate of activation between frozen-thawed and freshly collected oocytes and the majority of oocytes (> 90%) had a normal haploid chromosome constitution. The incidence of second polar body retention in frozen-thawed oocytes was low and did not differ significantly from that observed in fresh oocytes and oocytes exposed to dimethylsulfoxide (DMSO) at 0 degree C or 37 degrees C for extended periods beyond those required for protection. The frequency of aneuploidy was similar for frozen-thawed and fresh oocytes but oocytes held at 0 degree C without DMSO or held at 37 degrees C with DMSO for 1 hr showed a 2.5 and 12-fold increase in the frequency of aneuploidy compared with oocytes subjected to a conventional oocyte/embryo freezing regime. It is concluded that the procedures used in successful oocyte cryopreservation do not increase the incidence of chromosomal abnormalities of maternal origin in the resulting embryos.