Effect of Laser-Assisted Hatching on the Clinical Outcomes of Human Vitrified-Thawed Embryo Transfer Cycles with Different Post-Thaw Culture Duration
Authors: Luo Yang , Peng Fang , Sun Yuan , Li Lei 
Published: November 2020

Abstract
Background: Zona pellucida(ZP)hardening caused by prolonged in vitro culture and exacerbated by the freeze–thaw process making ZP hatching difficult; In theory, assisted hatching may facilitate the hatching process and have the potential to increase implantation and/or pregnancy rates in frozen embryo transfer (FET) cycles. However, a number of studies have shown controversial results on the clinical benefit of laser-assisted hatching (LAH) in FET cycles. This study firstly investigated the efficacy and safety of LAH using vitrified-thawed embryos with different post-thaw culture duration in FET cycles.Methods: Data from the center’s IVF database were retrospectively analyzed, only embryos thawed for the first FET cycle of each ovarian pick-up were eligible for this study, and only cycles in which at least one embryo was available for transfer were included in the present study. Finally, a total of 1225 infertile couples who underwent 1225 FET cycles between July 2013 and March 2015 were analyzed in this study. According to the duration of post-thaw culture in FET cycles, these patients were allocated to three subgroups: the short culture (4-5 h) group (LAH, n=205; control, n=201), overnight culture (20-24 h) group (LAH, n=197; control, n=203), and blastocyst culture (44-48 h) group (LAH, n=210; control, n=209), respectively.Results: In the short culture(4-5 h) subgroup, no statistically significant differences were found related to the implantation, clinical pregnancy and live birth rates between the two groups (28.0% versus 27.8%, 38.0% versus 36.8%, and 30.7% versus 30.3%, respectively, P＞0.05). When the perinatal outcomes of two groups were compared, there was no significant difference in the gestational weeks (37.96±2.23 versus 37.59±2.35, P＞0.05), birth weight (2.70±0.56 versus 2.82±0.62, P＞0.05), as well as the preterm birth (15.4% versus 17.6%, P＞0.05), ectopic pregnancy (2.6% versus 1.4%, P＞0.05), and miscarriage rates (16.7% versus 16.2%, P＞0.05).In the overnight culture(20-24 h) subgroup, no statistically significant differences were found regarding the implantation, clinical pregnancy and live birth rates (29.5% versus 29.1%, 40.1%versus 37.4%, 33.0%versus 30.5%, respectively, P＞0.05).As to the perinatal outcomes, there was no significant difference in the gestational weeks (36.86±2.28 versus 35.69±2.95, P＞0.05), birth weight (2.73±0.76 versus2.62±0.52, P＞0.05), as well as the preterm birth (15.2% versus 17.1%, P＞0.05), ectopic pregnancy (3.8% versus 2.6%, P＞0.05), and miscarriage rates (13.9% versus 15.8%, P＞0.05).In the blastocyst culture(44-48 h) subgroup, the two groups did not differ significantly in the implantation, clinical pregnancy and live birth rates (56.3% versus 59.3%, 68.6% versus 66.5%, and 55.7% versus56.5%, respectively, P＞0.05).Furthermore, there were also no significant difference in the gestational weeks (38.68±2.76 versus 36.95±2.59, P＞0.05), birth weight (2.78±0.74 versus 2.72±0.59, P＞0.05), as well as the preterm birth (8.3% versus 11.5%, P＞0.05), ectopic pregnancy (2.8% versus 2.2%, P＞0.05), and miscarriage rates (16.0% versus 12.9%, P＞0.05).Conclusions: Our results suggested that LAH does not improve the clinical outcomes in FET cycles, irrespective of the duration of post-thaw culture. Though the risk of perinatal period did not increase, it is still necessary to conduct further investigations to validate the safety of LAH.