Comparison of one-step and conventional warming in sibling donor oocytes: a proof-of-concept study

Are there differences in survival, embryo development and clinical outcomes between sibling oocytes warmed using one-step and conventional protocols?

A prospective, randomized, proof-of-concept trial using sibling donor oocytes to evaluate a one-step warming procedure. A total of 352 metaphase II oocytes (n = 30 donors) that had been previously vitrified using the conventional procedure were included. Just before warming, the oocytes were randomized into two groups: one-step warming (n = 179) and conventional warming (n = 173). The conventional warming protocol takes 10 min and involves three steps, using decreasing concentrations of trehalose. One-step warming only requires 1 min in 1.0 M trehalose solution. The main outcome was the survival rate. Fertilization rates, embryo quality, clinical results and oocyte developmental competence were also analysed.

The survival rate was 96.1% in the one-step warming group and 94.2% in the conventional-warming group, with no statistically significant difference. No differences were found when comparing the usable blastocyst rate (55.3% versus 52.1%) or good-quality blastocyst rate (46.1% versus 43.6%) of the one-step and conventional warming protocols, respectively. Similarly, no significant differences were found between implantation rates (69.2% versus 58.8%, respectively) and ongoing pregnancy rate per embryo transfer (53.8% versus 41.2%). The logistic regression analysis showed that the warming protocol did not correlate with ongoing pregnancy rate.

One-step warming can be safely applied to donor metaphase II oocytes, providing similar survival rates and clinical outcomes compared with conventional warming.