Day 2 versus day 3 embryo transfer in patients with fertilization and only one zygote with two pronuclei

Objective This study aimed to compare the pregnancy outcomes of Day 2 (D2) fresh embryo transfer and D3 fresh embryo transfer in women with only one zygote with two pronuclei (2PN). Methods Data on 432 in vitro fertilization-embryo transfer cycles with only one 2PN zygote from January 2016 to January 2022 were retrospectively collected. A total of 302 fresh embryo transfers on D2 (n = 193) and D3 (n = 109) were analyzed, and pregnancy outcomes were compared. Results The patients’ characteristics were not different between D2 and D3 embryo transfer. There were no significant differences in the rates of clinical pregnancy, early abortion, or live birth between D2 and D3 embryo transfer. A multivariate logistic regression model controlling for age, the fertilization method, the number of oocytes harvested, and the number of high-quality embryos transferred showed that the live birth rate was similar between D2 and D3 embryo transfer. Conclusion In in vitro fertilization-embryo transfer cycles with only one 2PN zygote, D2 fresh embryo transfer may provide similar pregnancy outcomes to those of D3 embryo transfer. D2 embryo transfer may be an option because of the risk of cycle cancellation due to the absence of viable embryos on D3.