Increased live births after day 5 versus day 6 transfers of vitrified-warmed blastocysts

Purpose

An investigation into the clinical implications of delayed blastulation (day 5 versus day 6) was carried out for cryo cycles, as heterogeneous results persist in the current literature.

Methods

We performed a retrospective study comparing clinical pregnancies and live births between 178 blastocysts vitrified and warmed on day 5 versus 149 on day 6. The stage of blastocyst development was taken into account and adjustment for confounding factors was performed.

Results

Our results demonstrate a significant difference in clinical pregnancy (43 versus 23% p value p value

Conclusions

Day of vitrification (day 5 versus day 6) appears to be an independent predictor of clinical outcomes. Stratification of our cohort was carried out according to the developmental stage, and significant differences persisted. Although the transfer of day 6 cryopreserved embryos remains a viable option, giving priority to a day 5 embryo would reduce the time to pregnancy.