Prolonged Culture of Blastocysts after Thawing as a Tool for Improving Prediction of Success

Introduction: A few years ago, we started to use a new freeze- thaw protocol for the FET cycles. Instead of thawing the embryos 2-4 hours prior to the transfer we started thawing the embryos 20-22 hours prior to the transfer.

Aim: The aim of this study was to compare the pregnancy rate in cases of embryos that continued to develop in the post-thawing culture to that of embryos that did not.

Materials and Methods: A single center, retrospective study of blastocyst freeze/thaw cycles vitrified on day 5, thawed and transferred after 20-22 hours in the culture, between January 2012 and December 2016.

Results: A total of 375 frozen, autologous cycles were included in the analysis. The age, number of eggs retrieved, and total number of blastocysts developed during the fresh cycle were comparable between the three groups. The clinical pregnancy rate (50% vs. 19.5% vs 3.3% p<0.01) and the ongoing pregnancy rate (38.5% vs. 13.6% vs 1.7% p<0.01) were higher in cases of good embryo quality compared with fair and poor quality embryos, respectively. For good embryos, progressing to a better grade during the culture did not change the clinical pregnancy rate (51.3% vs. 46.2% p=NS).For fair embryos, progressing to a better grade during the culture resulted in a higher pregnancy rate (26% vs 9% p<0.05).

Conclusions: The development of fair embryos to good embryos in the culture has a positive impact on the pregnancy rate. This factor should be taken into consideration before deciding how many embryos to transfer.