Late bloomers: exploring the reproductive potential of day 7 embryos

The purpose of this review is to evaluate the reproductive potential of day 7 embryos. With effective cryopreservation and subsequent frozen embryo transfers, extended blastocyst culture to day 7 is now possible. However, assessing the true reproductive potential of day 7 embryos is essential to adequately counsel patients on the expected pregnancy and live birth rates in comparison to embryos that reach the blastocyst stage on day 5 or day 6.

Day 7 embryos have a lower blastulation rate and higher aneuploidy rate compared with day 5 and day 6 embryos. Although day 7 blastocysts comprise less than 10% of usable embryos for transfer, recent studies have repeatedly demonstrated lower, but not negligible, pregnancy and live birth rates with day 7 embryo transfers. Based on the current literature reviewed in this paper, the clinical pregnancy rates for euploid day 7 embryos appear to be between 16.7 and 52.6%, whereas the live birth rates are between 21.5 and 46%. Therefore, while the blastulation and pregnancy rates are lower and the aneuploidy rates are higher, euploid day 7 embryos have reproductive potential.

While recent data supports reduced reproductive potential of euploid day 7 embryos when compared with the success rates of day 5 and 6 embryos, their associated pregnancy and live birth rates are nonzero and still represent a viable option for certain patients.