Background: Freezing/vitrifying and thawing/warming of embryos may impair the successful hatching process of the embryo out of its zona pellucida (ZP) and its following implantation into the uterus. Theoretically, assisted hatching (AH) may facilitate the hatching process and subsequently increase implantation rates (IRs).
Methods: In this prospective randomized controlled trial (RCT), the hypothesis was tested that the IR per embryo transferred is higher after transfer (ET) of frozen/vitrified-thawed/warmed embryos with thinned ZP after AH by modified quarter laser-assisted zona thinning (mQLAZT) when compared with ET of frozen/vitrified-thawed/warmed embryos without mQLAZT. Patients with frozen/vitrified embryos were randomized at the time of thawing/warming to a study group (with mQLAZT) or a control group (without mQLAZT). After thawing/warming, embryos were kept in culture for 24h, and mQLAZT was performed prior to ET.
Results: A total of 647 thawing cycles were randomized to either the mQLAZT group (n = 324) or the control group (n = 323). Reproductive outcome data were available for 302 cycles in the mQLAZT group and 317 cycles in the control group. Transfer could be performed in 73.5% and in 71.9% of the thawing/warming cycles in the mQLAZT group and the control group (P = 0.78), respectively. No significant differences were observed between the mQLAZT group and the control group for the IR [13.3%; 15.6%; rate ratio 0.85; 95% confidence interval (CI), 0.596-1.224], the ongoing IR (10.5 and 13.5%, P = 0.25) and the live birth rate [10.5%;13.3%; rate ratio 0.79; (95% CI), 0.530-1.189] per embryo transferred.
Conclusions: In this RCT, mQLAZT did not improve the IR per embryo transferred in frozen/vitrified-thawed/warmed embryo transfer cycles. ClinicalTrials.govID NCT00593775.