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

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. 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. Implantation rates, pregnancy rates, ongoing pregnancy rates, and live birth rates in the first 2 groups were almost double the rates in the third group. The figures for implantation rates were 40 \% in the first two groups vs. 19 \% in the third group (P < 0.05). Pregnancy rates were 60.9 \% and 64 \% vs. 31.8 \% (P < 0.05) and ongoing pregnancy/ live-birth rates were 52.3 \% \& 56 \% vs. 27.3 \%. The current study reports better implantation and pregnancy rates with earlier expanding blastocysts regardless of the time of transfer.