Cumulative Live Birth Rates After Cleavage-stage Versus Blastocyst-stage Embryo Transfer: A Multicenter, Prospective, Randomized Controlled Trial

This is a multicenter, randomized clinical trial comparing the efficacy and safety between cleavage-stage embryo transfer and blastocyst-stage embryo transfer in IVF/ICSI treatment cycle, taking into account of subsequent vitrified embryo transfers.Randomization will be performed on day 2/3 after oocyte retrieval, when at least 3 embryos are achieved. Patients in group A will have 1 cleavage-stage embryo transferred. Patients in group B will have 1 blastocyst-stage embryo transferred. The outcomes from all the embryo transfers within 1 year after randomization will be followed up. If a pregnancy/live birth is not achieved, single embryo transfer is required for the first 3 embryo transfers within 1 year after randomization. For embryo transfers beyond the third within the 1 year, patient's treatment must follow their randomized allocation, and SET is no longer mandatory. The follow-up period is 2 years from the day of randomization.Due to the COVID-19 pandemic, the participants who were unable to undergo the embryo transfers in 1 year of randomization will have 3 months extension for frozen embryo transfer. The follow-up for these participants will be extended for 3 months as well.