Increased live births after day 5 versus day 6 transfers of vitrified-warmed blastocysts
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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.
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.
Our results demonstrate a significant difference in clinical pregnancy (43 versus 23% p value < 0.001) and live birth rates (34 versus 16% p value < 0.001) regarding the day of vitrification, in favour of day 5. This difference persisted after adjustment for confounding factors. The adjusted odds ratio for clinical pregnancies and deliveries for the day 5 group compared to that of the day 6 group was 2.83 (95%CI, 1.48 to 5.41) and 2.94 (95%CI, 1.39 to 6.22), respectively. When the stage of development of the blastocyst was taken into consideration, we still observed a significant advantage of day 5 versus day 6 vitrification.
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.
KeywordsBlastocyst Vitrification Day 5 Day 6 Live births Assisted reproduction
The authors are grateful to the CHU St-Pierre IVF team and Pierre Vanderzwalmen for participating in scientific discussions.
Compliance with ethical standards
All our protocols have been approved by the local Ethics Committee and all our patients have given their informed, written consent prior to treatment. The current study was approved by the Ethics Committee of the CHU St-Pierre (AK/16-11-139/4734).
Conflict of interest
The authors declare that they have no conflict of interest.
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