Background: In thawed embryo transfer cycles, the most common method is to transfer the embryos after 2 h of culture. Clinical outcomes of frozen-thawed cleavage embryo transfer cycles regarding the embryos status and the culture time of frozen-thawed cleavage embryos were limited and did not elucidate all unclear issues.
Objectives: The objective of this study was to examine the clinical outcomes of frozen-thawed cleavage embryo transfer cycles according to the embryos status and the culture time (2 h or overnight).
Material and methods: In this retrospective study (5-year period), 1,654 frozen-thawed embryos were analyzed. Firstly, frozen-thawed cleavage embryos were divided into 2 groups according to their status as follows: with at least 1 optimal embryo and without optimal embryos. Secondly, both of them were divided into 2 groups according to the culture time (2 h or overnight). Age of the female, infertility factors, clinical pregnancy, implantation rate, and live birth rate were compared.
Results: There were no statistically significant differences in the pregnancy rate, the implantation rate, live birth rate, the miscarriage rate, and the ectopic pregnancy rate in each group. However, the implantation rate increased after 2 h of incubation (41.1%) compared to overnight incubation (36.0%) in the group with at least 1 optimal day-3 embryo (p < 0.05). The cancellation rate in the suboptimal day-3 embryos group (9.1%) was higher than in the group containing at least 1 optimal embryo (0.2%) for the long (overnight) culture (p < 0.05).
Conclusions: The implantation rate can be improved in the optimal day-3 embryos transferred after 2 h of culture, but not for suboptimal day-3 embryos. Some unnecessary transfers can be avoided after overnight culture because of no further cleavage of the embryos.
Keywords: assisted reproductive technology; clinical outcomes; embryo transfer; frozen–thawed; vitrification.