Study question: Is the transfer of a frozen thawed blastocyst in an artificial cycle associated with higher implantation and ongoing pregnancy rates than fresh blastocyst transfer in a stimulated cycle?
Summary answer: Frozen thawed transfer (FET) of euploid blastocysts in an artificial cycle seems to yield significantly higher implantation, clinical and ongoing pregnancy rates than fresh transfer of euploid blastocysts in the stimulated cycle.
What is known already: Some data suggesting FET is associated with better clinical outcome than fresh transfers. Endometrial receptivity is thought to be disrupted by high estradiol levels during stimulation. However the quality of evidence is low to moderate, and generalizability of the findings is questionable. There's a need for properly sized randomized controlled trials controlling for other factors including embryo aneuploidy.
Study design, size, duration: Planned interim analysis of a randomized controlled trial, including 76 women over one year of recruitment. The study is halfway at the time of submission. We expect to have results from over 100 women by the time of conference.
Participants/materials, setting, methods: Women <42 without poor ovarian reserve or azospermic partner were randomized to fresh transfer or FET. Assisted hatching was on day 3, and trophoectoderm biopsy was done on day 5 or 6. Comprehensive chromosome screening was by next generation sequencing (Ion Torrent PGM). Only euploid blastocysts were transferred.
Main results and the role of chance: Fresh and FET groups included 37 and 39 women, respectively. 15 women in the fresh group had no fresh transfer (13 had no euploid embryos, 2 other reasons). 31 women in the FET group were available for analysis (8 awaiting FET presently). Five women in FET group had no euploid embryos. Baseline and stimulation cycle parameters including number of blastocysts transferred were similar. Ongoing pregnancy rates (OPR) were 14/37 (38%) vs 20/31 (65%), in the fresh and FET groups, respectively (p=0.03). Per protocol analysis revealed OPR of 14/22 (64%) vs 21/27 (78%), in the fresh and FET groups, respectively (p=0.23). Implantation rates were 67% vs 82%, difference was not statistically significant but was in favor of FET (p=0.23).
Limitations, reason for caution: The observed differences can change when the trial is completed.
Wider implications of the findings: In this trial effect of fresh transfer on endometrial receptivity is almost isolated as embryonic aneuploidy is eliminated through CCS. If the difference in favor of FET is maintained, this finding can change practice worldwide. FET with CCS can enable single embryo transfer with excellent pregnancy rates.
Study funding/competing interest(s) Funded by by hospital/clinic(s), Funding by commercial/corporate company(ies) – Life; Technologies; Oregon Reproductive Medicine; Reprogenetics
Trial registration number NCT02000349