Similar delivery rates in a selected group of patients, for day 2 and day 5 embryos both cultured in sequential medium: a randomized study.

Background: The existence of a real benefit of blastocyst transfer is still a matter of debate. The aim of this study was to compare, in a prospective randomized trial, the outcome of day 2 and day 5 transfer of human embryos cultured in an 'in-house' sequential medium.

Methods: A total of 193 cycles from 171 patients with less than four previous IVF cycles, <39 years old and with four or more zygotes on day 1, were randomly allocated to day 2 (94 cycles) or day 5 (99 cycles) transfer. Zygotes were kept in fertilization medium until 18 h post-fertilization and then placed in a 'glucose-free' cleavage medium. Embryos allocated for day 5 transfer were placed in a blastocyst medium 66 h post-fertilization. Two or three embryos were replaced according to the morphology.

Results: A mean (+/- SEM) number of 2.1 +/- 0.4 and 1.9 +/- 0.3 embryos were replaced on day 2 and day 5 (P < 0.001) respectively. Delivery rates per transfer were 44.1 and 37.1% [P = not significant (NS)], implantation rates were 31.4 and 29.4% (NS) and multiple delivery rates 22 and 36% (NS) for day 2 and day 5 groups respectively. Ten patients (10.1%) had no blastocysts available for transfer.

Conclusions: No clear benefits were observed using blastocyst transfer for patients aged <39 years who had had less than four previous IVF cycle attempts.