Giant oocytes in human in vitro fertilization treatments

Giant oocytes are potential sources of chromosomal abnormalities and should thus never be used in in vitro fertilization and embryo transfer (IVF-ET) procedures. The presence of giant oocytes may indicate the efficiency of the ovarian stimulation and can refer to the quality of sibling oocytes.

IVF cycles performed between January 2008 and November 2013 (n = 1521) were divided into two groups: Giant Oocyte Group (GO Group) contained cycles with at least one giant oocyte in the cohort of the retrieved oocytes (n = 37), Normal Group contained cycles with no giant oocytes (n = 1484). In the second part of the study, cycles from GO Group and Normal Group were matched according to patient age, number of retrieved oocytes and stimulation protocol, and thus 30 pairs were formed. Clinical and embryological data were analyzed.

The incidence of giant oocytes was 0.3 %. The average patient age was lower (33.5 ± 3.9 vs. 35.3 ± 4.9, p = 0.02); estradiol (E2) levels (1954 ± 903 vs. 1488 ± 909 pg/l, p < 0.01) and number of retrieved oocytes (12.7 ± vs 8.1 ± 5.1, p < 0.01) were significantly higher in the GO Group. There was no difference in clinical pregnancy rates (37.8 vs. 37.4 %, p = 1.00) between the two groups. No major differences in the embryo qualities were found. In the second part of the study, fertilization rate in the matched GO Group was lower (50.6 ± 21.9 vs. 61.9 ± 22.4 %, p = 0.04). Clinical pregnancy rates (36.7 vs. 36.7 %, p = 1.00) did not differ between the matched cycles.

Our data suggest that the stimulation protocol does not affect the incidence of giant oocytes. Giant oocytes present in cycles with higher number of retrieved oocytes in younger women. The presence of these gametes does not refer to the quality of sibling oocytes and embryos, or the outcome of the treatment.