Preimplantation genetic screening (PGS) in egg donor (ED) cycles: is it a valid option?

Abstract

A recent study demonstrates a high variability among different centers in the euploidy rate of embryos generated from donated eggs (Munnè et al., 2017). Using SNP array analysis, most embryonic meiotic aneuploidies have been found to be from maternal origin. From these observations, it may be speculated that the ovarian stimulation may affect the embryo euploidy rate independently from the oocyte source. Despite this, PGS in ED cycles is often considered unnecessary. Very few studies examined the use of PGS in ED cycles thus far and the results were inconclusive. In order to investigate the utility of PGS in ED cycles, we compared the clinical outcomes of frozen embryo transfers (FET) cycles involving oocyte donation in which PGS was performed to controls in which PGS was not used. This is a retrospective, single-center cohort study. 622 FET cycles with embryo derived from donated eggs, conducted between 1 January 2015 and 31 December 2016, were included. In 570 cycles the embryos were tested by PGS and in 52 cycles the embryos were not tested. In order to have a group as homogenous as possible, only the first FET cycle from freeze-all cycles (Cryotech Vitrification and Warming®) was considered. Both NGS and aCGH were used for the genetic screening. 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) between the PGS and no-PGS groups and of 12% among the PGS subgroups. The results are reported in Table I. The percentage of euploid blastocyst from egg donors was 54.6%; the aneuploid blastocysts 30.9% and the mosaic blastocysts 13.9%. No results were 0.6%.Table IClinical outcome of FET cycles involving oocyte donation with and without PGSNo-PGS totPGS totNo-PGS single ETPGS single ETNo PGS ≥ 2 ETPGS ≥ 2 ETP valueET Cycles525701532937241Egg donor age25.5±2.925.5±2.925.6±3.1Survival rate after thawing98.0%97.6%88.9%97.3%100%97.8%Average n of euploid embryos-4.9±3.7-4.7±3.8*-5.6±3.4**p=0.006Average n of emb transferred1.8± 0.6*1.4±0.5*1.0±0.01.0±0.02.1±0.42.0±0.2*p=0.0003Ongoing PR57.7%57.2%20.0%*50.5%* ** ***72.9%**64.7%**** p=0.032 **p=0.009 ***p=0.0008Ongoing IR40.9%47.2%20.0%*50.5%*44.9%42.4%*p=0.032AR10.0%9.5%0.0%11.4%11.1%7.1%Twin rate26.7%19.0%0%0%* **29.6%*34.0%***p=0.0001 **p=0.0001PR: Pregnancy Rate, IR: Implantation Rate; AR: Abortion Rate Open table in a new tab PR: Pregnancy Rate, IR: Implantation Rate; AR: Abortion Rate Considering only the first FET cycle with embryos derived from donated eggs, we found a significant increase in the ongoing pregnancy and implantation rate in cases of single embryo transfer in the PGS group compared with the non-tested group. Transferring ≥2 embryos statistically increased the ongoing pregnancy but also the twin rate in both PGS and no-PGS group compared to the single embryo transfer, and no differences between the PGS and the control group were found. In terms of chances of achieving a single pregnancy in the first FET attempt, the PGS seems to have a valid role also in ED cycles. Transferring ≥2 embryos may overcome the advantage of the PGS but twin rates is high.