Effect of embryo transfer difficulty on live birth rates studied in vitrified-warmed euploid blastocyst transfers

Research question: The aim of this study was to investigate the relationship between the different manoeuvres employed or degrees of difficulty during embryo transfer and live birth rate (LBR) in frozen euploid (blastocyst) embryo transfer (FEET). Design: A retrospective, observational study of women undergoing FEET was performed. If the catheter encountered any resistance in its passage through the cervix, a stepwise approach was used. Easy embryo transfer was defined as a direct embryo transfer or use of the outer sheath of the catheter. Difficult embryo transfer was defined as when the process required the use of a Wallace Malleable Stylet (Smiths Medical International Ltd., UK) without or with additional instrumentation such as a tenaculum or uterine sound. Results: The analysis involved 370 FEET. LBR was significantly lower in difficult FEET procedures compared with easy ones (54.5% versus 40.5%, P = 0.026) but significance was lost after adjustment for confounders. Use of the outer sheath use did not affect LBR. Although LBR was significantly lower when the stylet, without or with a tenaculum, was required (odds ratio [OR] 0.56, 95% confidence interval [CI] 0.34-0.93; P < 0.05), no statistically significant reduction was observed after adjustment for confounders (OR 0.81, 95% CI 0.45-1.47). Conclusions: No significant reduction in LBR was observed after adjustment for confounders between difficult and easy FEET, or when use of stylet without or with a tenaculum was required for embryo transfer. The lack of significance may be due to factors such as the sample size or the use of array comparative genomic hybridization analysis. Further studies are needed to confirm these results.