The impact of cryopreservation on biopsied embryos without the bias of the uterine receptivity. retrospective analysis of 493 PGS cycles involving egg donors (ED)/gestational carriers (GC)

Abstract

PGS often requires cryopreservation of embryos after biopsy. The transfer of frozen embryos into a uterus not affected from ovarian stimulation might result in a greater pregnancy rate (PR), as recent studies support the benefit of the freeze-all policy in the PGS cycles. However, cryopreservation itself may still entail some risk to the biopsied embryo. Due to the confounding uterine factor, the possible damage of the cryopreservation on biopsied embryos might have been underestimated. In this study we investigated the impact of cryopreservation on the clinical outcome of PGS cycles. In order to eliminate any bias related to the uterine receptivity, we compared fresh and frozen PGS cycles, in which only ED and GC were used. This is a retrospective, single-center cohort study including PGS cycles in which both, ED and GC where involved. 493 embryo transfer ET cycles conducted between 1 January 2015 and 31 December 2016 were included, of these, 63 were fresh ET and 430 were frozen ET (FET) from freeze-all cycles (Cryotech Vitrification and Warming®). Only the first FET cycle was considered. In each cycle an ED and GC were used. The embryos frozen on D5 were thawed either on the afternoon before the ET, or on the ET day based on the Lab workload. D6 embryos were thawed on the ET day. FETs were conducted after endometrial priming with estradiol. Setting the α error at 0.05, our study had a power of 80% to observe a decrease of 20% in the ongoing pregnancy and implantation rate (G*power 3, post hoc analysis). The results are reported in Table ITable IClinical outcomes of fresh versus frozen embryo transfers in PGS cycles involving both ED and GC.Fresh Embryo TransfersFrozen Embryo TransfersTotalD5 embryos cultured overnight after thawingD5 embryos cultured few hours after thawingD6 embryos cultured few hours after thawingN634304035535Donor age26.3 ± 3,625.5 ± 2.925.4 ± 2.825.5 ± 3.025.4 ± 2.7n of embryos biopsied9.0 ± 4.48.0 ± 3.98.5 ± 3.37.8 ± 3.38.1 ± 4.9survival rate-95.8%95.3%95.8%96.8%n of embryos transferred1.7 ± 0.6*1.4 ± 0.5*1.3 ± 0.61.4 ± 0.51.7 ± 0.7Ongoing PR69.8%62.1%57.5%62.8%57.1%Ongoing IR55.9%51.4%**50.9%54.2%37.9%**AR7%10.1%8.7%10.3%10.6%* p = 0.0026, **p=0.026; PR: Pregnancy Rate, IR: Implantation Rate; AR: Abortion RateAlthough the number of embryos transferred in the fresh group was statistically higher, we did not observe any decrease in the clinical outcomes of the frozen group. D6 thawed embryos implanted at a lower rate. Open table in a new tab * p = 0.0026, **p=0.026; PR: Pregnancy Rate, IR: Implantation Rate; AR: Abortion Rate Although the number of embryos transferred in the fresh group was statistically higher, we did not observe any decrease in the clinical outcomes of the frozen group. D6 thawed embryos implanted at a lower rate. To best of our knowledge, our study is the first that compares fresh and frozen PGS cycles in which both, ED and GC were involved, eliminating the bias of the improved uterine receptivity in the FET cycles. With the limitation of a study powered to detect as significant a reduction of 20% in the ongoing PR and IR, the cryopreservation itself seems not to have a negative impact on the clinical outcome of the PGS cycles. When a patient had only D6 embryos for the FET, the implantation rate was lower.