Successful introduction of a one-step blastocyst warming protocol: a UK multicentre large cohort comparison

Can a one-step warming (OSW) protocol for vitrified blastocysts be an effective and efficient alternative to standard warming while yielding similar or improved clinical outcomes in a multicentre setting?

Retrospective study analysing data from 15 clinics; 3 months of data using a standard warming protocol were compared with 3 months using a OSW protocol. For comparison of survival rates, all warmed day-5 and day-6 blastocysts were analysed. For clinical outcomes, data were corrected for age (<38 years at the time of vitrification), not tested for preimplantation genetic testing (PGT), autologous oocytes and single blastocyst transfers. Standard warming protocol: embryos were incubated for 1 min in thawing solution, 3 min in dilution solution, 5 min in washing solution and 1 min in washing solution 2 before being transferred into culture medium; OSW protocol: 1 min thawing solution, then transferred into culture medium, as above.

A total of 3887 blastocysts were warmed, with a significantly higher survival rate after OSW (97.7%) than after standard warming (95.9%; chi-squared[1] = 10.84, P = 0.013). No significant differences were observed in clinical pregnancy rates (OSW: 44.7%; standard warming: 41.2%; P = 0.088) or live birth rates among cycles with a recorded final outcome (OSW: 35.8%; standard warming: 36.1%; P = 0.946).

One-step warming protocols improve blastocyst survival rates with no effect on clinical outcomes. Standard warming takes about 10 times longer per embryo than the OSW protocol, which enables clinics to significantly improve laboratory efficiency and resource management without compromising patient care.