Objective: To evaluate the development potential and clinical significance of day 3 4-cell embryos after extended in vitro culture.
Methods: This study was a retrospective cohort study for patients with infertility treatment between January 2011 and July 2013. Patients undergoing blastocyst culture in controlled ovarian hyperstimulation cycles using surplus embryos were analyzed in the study. A total of 764 women undergoing blastocyst culture with 1,522 surplus 4-cell embryos on day 3 were analyzed. An additional 2,391 patients with embryos undergoing blastocyst culture during the same period with embryos having more blastomeres were chosen as control.
Results: After extended culture, 253 embryos from 183 cycles in the study group which developed to blastocysts were frozen, and 118 embryos were warmed in subsequent frozen embryo transfer cycles. Implantation rates, clinical pregnancy rates (PRs) and ongoing PRs were 33.3 %, 38.4 % and 31.4 %, respectively, which were similar to those of the control group. The singleton birth weights of newborns using these blastocysts showed no significant difference to that seen in the control group.
Conclusion: Surplus 4-cell embryos on day 3 displayed lower blastulation rates. However, once a blastocyst is obtained, it has equivalent clinical outcomes. Embryos that are developmentally lagging on day 3 can be observed in extended culture to increase the cumulative chances of a successful pregnancy.