Thawing day 3 embryos and culturing to day 5 may be a better method for frozen embryo transfer.

ABSTRACT

PURPOSE: Does thawing cleavage embryos and culturing them for transfer as blastocysts improve pregnancy and perinatal outcomes compared to transferring thawed blastocysts? METHODS: Retrospective, observational cohort study performed at two assisted reproductive technology centers, 2014 to 2020. A total of 450 patients with 463 thawed embryo transfer cycles were divided into 2 groups according to the embryonic developmental stage at cryopreservation and transfer 231 thawed blastocysts (day 5 group) and 232 thawed cleavage embryos that were cultured for 2 days and transferred as blastocysts (day 3-5 group). The two groups were compared for demographics, routine parameters of IVF treatment, pregnancy rates, and perinatal outcomes. RESULTS: Multivariable logistic regression analysis for ongoing pregnancy and delivery demonstrated that the day 3-5 group had a greater likelihood of achieving ongoing pregnancy and delivery compared to the day 5 group (OR 1.58, 95%CI 1.062-2.361, p = 0.024). Perinatal outcomes were comparable between the three groups. CONCLUSION: Our results support culturing post-thaw cleavage embryos for 2 days and transferring them as blastocysts to increase chances of ongoing pregnancy and delivery.