Do faster, do better: frozen embryo transfer outcomes with one-step warming protocol at different embryos stages

What effect does the use of a rapid warming method of vitrified embryos have on survival and pregnancy?

A comparison of two different warming embryos protocols: long protocol (group 1, n = 486) and a new fast protocol (group 2, n = 413) for blastocyst and cleavage stage frozen embryo transfers at two IVF centres: Assisted Reproductive Technology Centre, Careggi University Hospital Firenze and IVF Unit, 'Cervesi' Hospital Cattolica. Total pregnancy rate was considered primary outcome, and embryo survival rate, clinical pregnancy rate, miscarriage rate, ongoing pregnancy rate and mean time required for warming procedure were considered secondary outcomes.

The same embryo survival rate was observed in the two groups. Total and clinical pregnancy rates seemed to be higher, but not statistically different, in group 2 compared with group 1 (29.5% versus 26.7% and 27.6% versus 22.6%, respectively). Conversely, a statistically significant reduction in miscarriage rate was found in group 2 compared with group 1 (18.0% versus 32.3%, P = 0.009). Similarly, a significant increase in pregnancy rate at 26 gestational weeks or over was observed in group 2 compared with group 1 (66.9% versus 80.3%, P = 0.016). Finally, a difference in time required for warming procedures was found in favour of group 2.

The use of the fast warming protocol is a valid alternative to the classic warming protocol, and allows a reduction in the time needed to carry out the procedure and the workload of embryologists in an IVF laboratory.