Day 5 expanded blastocysts transferred on same day have comparable outcome to those left for more extended culture and transferred on day 6.

Objective: To study the outcome of blastocysts showing expansion on day 5 and transferred on day 5 or 6, in comparison with those unexpanded and transferred on day 6.

Study Design: Prospective cohort of 221 women prepared for BET classified into three groups according to timing of blastocyst expansion and day of embryo transfer. Group I; with expanded blastocysts on day 5 having day 5 transfer, group II; with expanded blastocysts on day 5 having day 6 transfer and group III ; with delayed expansion undergoing day 6 BET.