The incidence of chromosomal abnormalities in frozen—thawed mouse oocytes after in-vitro fertilization

Abstract

Cryopreservation of mouse oocytes induced a high rate of atresia. Frozen oocytes observed immediately after thawing did not exhibit any alteration in the frequency of chromosomal abnormalities, aneuploidy or polyploidy. After in-vitro fertilization attempts, the cleavage rate of frozen-thawed mouse oocytes was decreased. Cytogenetical observations of inseminated eggs also confirmed this decrease in fertilization rate. First and second cleavages were delayed compared to fresh controls but subsequent development to the 4-cell stage was not altered. Freeze-thawing increased the incidence of chromosomal abnormalities in inseminated oocytes but this only concerned the frequency of triploidy and not monosomic or trisomic aneuploidy. The increase in triploidy seemed to be largely due to the presence of digynic embryos. Second polar body retention seemed to be mainly responsible for this high rate of polyploidy.

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

“…In agreement with several previous cytogenetic studies (Glenister et al, 1987;Bouquet et al, 1992) we did not detect any significant increase in the frequency of aneuploidy when oocytes were submitted to similar slow-freezing methods. Also, the incidence was no different from that observed after fertilization in vivo (Kaufman, 1973).…”

“…Using low temperatures without cryoprotectant or exposing oocytes to cryoprotectant a t high temperatures are deleterious. Moreover, in our parthenogenetic system we did not detect any increase in the retention of a second polar body, as suggested before (Glenister et al, 1987;Carroll et al, 1989;Bouquet et al, 1992Bouquet et al, , 1995. However, the relatively high frequency (2-3%) with which this abnormality occurs in human fertilization (Boue et al, 1975) stresses the need of a careful evaluation of in vitro fertilized human embryos at the pronucleus stage before transfer to avoid the risk of polyspermy.…”

“…In previous studies on the cytogenetic analysis of embryos obtained from frozen-thawed mouse oocytes after in vitro fertilization, Glenister et al (1987) and Bouquet et al (1992) found that there was no significant difference in the incidence of aneuploidy at first cleavage when compared with nonfrozen controls. In contrast, Kola et al (1988) after analyzing a much smaller sample of mouse embryos at first cleavage detected almost a three fold increase in aneuploidy in embryos derived from frozen-thawed oocytes.…”

Effects of cooling and equilibration in DMSO, and cryopreservation of mouse oocytes, on the rates of in vitro fertilization, development, and chromosomal abnormalities

“…This observation is in agreement with the fact that after the freezing-thawing of OOCyteS, the derived embryos do not present higher aneuploidy rate than control embryos (Glenister et al, 1987;Bouquet et al, 1992;present study). The discordance between these results and immunocytochemical observations which showed that DMSO and cooling were responsible for chromosomal dispersion, possibly leading to aneuploidy Pickering and Johnson, 1987), might be explained by the fact that our study was performed on one-cell fertilized oocytes, and the others on unfertilized oocytes.…”

“…Contrary to the complete cryopreservation process (Kola et al, 1988;Carroll et al, 1989;Bouquet et al, 1992; present study), the exposure of oocytes to cooling to 0°C and/or to DMSO does not induce an increased total number of morphological abnormalities. This result, which is in accordance with the observations of Glenister et al (1987), suggests that the important cellular damage after oocyte cryopreservation is due to events taking place at the time of freezing from 0°C to -196°C andlor thawing.…”