Effect of Cryopreservation of Sibling 2PN Zygotes on Cumulative Delivery Rates in the Human IVF-ET Program

Kim, Myo Kyung; Lee, Sun Hee; Choi, Su Jin; Choi, Hye Won; Park, Dong Wook; Lim, Chun Kyu; Song, In Ok; Lee, Hyoung Song

Abstract

OBJECTIVE
This study was carried out to know whether cryopreservation of sibling 2PN zygotes could increase the cumulative delivery rates in the patients who had less than 10 fertilized zygotes.
METHODS
A retrospective analysis was performed in 138 in vitro fertilization-embryo transfer (IVF-ET) cycles with less than 10 fertilized zygotes during January 2003 to December 2007 in Cheil General Hospital. These cycles were divided into two groups. In Group I (n=86), all fertilized embryos were cultured to transfer on day 3 without cryopreserved embryos at the 2PN stage. In Group II (n=52), among fertilized zygotes, some sibling zygotes were frozen at the 2PN stage, the remainder were cultured to transfer. Clinical outcomes in fresh ET cycles and cumulative ongoing pregnancy rates after subsequent frozen-thawed (FT)-ET cycles were compared.
RESULTS
There were no significant differences in female mean age, number of retrieved oocytes and total fertilized embryos between two groups. Number of cultured embryos was significantly lower in Group II (5.2+/-0.5) than in Group I (8.4+/-0.7) (p<0.01). Also, number of transferred embryos was significantly lower in Group II (3.3+/-0.6) compared with Group I (3.6+/-0.6) (p<0.01). beta-hCG positive rates and delivery rates (51.2 vs. 46.2% and 41.9 vs. 34.6%, respectively) after fresh ET were slightly higher in Group I than in Group II. However, the differences were not statistically significant. Also, the cumulative delivery rates after subsequent FT-ET cycles were not significantly different between Group I (48.8%) and Group II (50.0%).
CONCLUSION
This study showed that cryopreservation of sibling 2PN zygotes from patients who had less than 10 zygotes in the fresh ET cycles did not increase cumulative delivery outcomes. But, it could provide an alternative choice for patients due to offering more chance for embryo transfers if pregnancy was failed in fresh IVF-ET cycles.