Impact of post-warming culture duration on clinical outcomes of vitrified good-quality blastocyst transfers: a prospective randomized study

Objective: To determine whether post-warming culture duration (1 hour vs. 18 hours) influences implantation rates (IRs) of good-quality blastocysts (GQB) in a good-prognosis population.

Design: Prospective interventional randomized study.

Setting: University hospital.

Patient(s): One hundred sixty-two GQB transfers.

Intervention(s): Patients' vitrified blastocysts were randomly allocated to group A, warming on the day before transfer (n = 81), or B, warming on the day of transfer (n = 81).

Main outcome measure(s): IR, live birth rate, reexpansion degree, and quality after warming and immediately before transfer.

Result(s): Quality of the warmed and transferred blastocysts was similar (respectively, 39.1% and 32.7% top quality [≥B4AA/AB/BA] in group A vs. 41.7 and 42.2% in group B). In group A, 14 of 102 blastocysts (12.2%) appeared to be unsuitable for transfer, versus only 1 of 103 (0.9%) in group B, thus leading to an additional warming. As expected, reexpansion degree just before transfer was higher in group A (0.90 vs. 0.70). Likewise, the proportion of hatched blastocysts before transfer was higher after a longer culture period (38.6% in group A vs. 12.7% in group B). IRs were similar (38.0% in group A vs. 36% in group B), as were live birth rates (35.8% in group A vs. 34.6% in group B).

Conclusion(s): IRs were not different, whatever the duration of post-warming culture of GQB. Both warming strategies could be applied to good-prognosis patients to optimize the laboratory workflow without any detrimental effect.