Does The Culture of Post-Thawed Cleavage-Stage Embryos to Blastocysts Improve Infertility Treatment Outcomes of Frozen-Thawed Embryo Transfer Cycles? A Randomised Clinical Trial

Background: There is a definite shift in assisted reproductive centres from cleavage-stage embryo transfer (ET) toblastocyst transfer that is attributed to improvements in laboratory environments and advances in the development ofembryo culture media. The aim of the study was to investigate the reproductive outcomes of thawed cleavage-stage ET versusblastocysts derived from an extended culture of these embryos. Materials and Methods: This open-label, randomised, parallel group clinical trial study enrolled 182 women aged ≤37 years who underwent frozen-thawed ET from November 2015 to June 2020 at Royan Institute Research Centre, Tehran,Iran. The women were randomly assigned to either the thawed cleavage ET group (n=110) or the post-thaw extended cultureblastocysts group (n=72). The primary outcome measure was the clinical pregnancy rate. Secondary outcome measureswere implantation rate, live birth rate (LBR), and miscarriage rate. A P 0.05 indicated statistical significance. Results: There were no significant differences between the two groups in terms of demographic characteristics. Boththe mean numbers of embryos transferred and good quality embryos transferred were significantly lower in the post-thawextended culture blastocysts group compared to thawed cleavage-stage ET cycles. However, the post-thaw extendedculture blastocysts group had higher clinical pregnancy (56.94 vs. 40.91%, P=0.034), implantation (34.43 vs.19.84%, P=0.001) and live birth (49.3 vs. 33.63%, P=0.036) rates compared to the thawed cleavage-stage ET group. Miscarriage and multiple gestations rates were comparable between the groups. Conclusion: These results allow us to take a position in favour of post-thaw extended culture blastocysts; thus, it isimportant to improve the post-thawing extended culture technique (registration number: NCT02681029).