P-755 Timeless importance of the embryo transfer technique: a real-life retrospective study comparing direct versus afterload catheters
Authors: Cirillo F , Immediata V , Carletti T , Ronchetti C , Morenghi E , Albani E , Baggiani A , Levi-Setti P E 
Published: June 2023

Abstract

Study question
Can the embryo transfer (ET) technique influence clinical pregnancy rate (CPR)?

Summary answer
Our study demonstrated that CPR is significantly affected by the ET technique. In particular, with the afterload technique both CPR and easy transfer rates increased.

What is known already
Despite it having widely demonstrated that the occurrence of difficult ETs reduces the success of assisted reproductive technology (ART) cycles and that afterload technique has showed a decrease in the number of difficult transfers compared to the direct one, few data are available assessing pregnancy outcomes in the two different techniques. The present study represents the progression of a published prospective randomized controlled trial (RCT) performed in the same setting on a smaller population comparing direct and afterload techniques on the difficult transfer rate, but not designed to demonstrate differences in terms of CPR.

Study design, size, duration
Single center retrospective cohort analysis of 8,189 fresh and frozen single blastocyst transfers performed between January 2016 and December 2021 in a tertiary University affiliated fertility center. Of the total, 2,000 ETs were performed with the direct technique and 6,189 with the afterload one. All fresh single day-5 and single day-5 and day-6 frozen blastocyst transfers performed during the study timeframe were included.

Participants/materials, setting, methods
Direct technique was the only one used from January 2016 to September 2017. In the clinical trial recruitment period, the choice was given by randomization. From April 2019, only the afterload technique was used: the operator never had chance to choose the technique. Preimplantation genetic testing cycles, gamete donation and day-7 blastocyst transfers were excluded. CPR was the primary outcome, while difficult transfer rate the secondary one. Univariate and multivariate logistic regression have been performed.

Main results and the role of chance
During the period, 8,189 single blastocyst transfers were performed. Afterload ET showed a percentage of difficult transfers which was almost one third compared to that of the direct ET, being respectively 9.06% and 26.85% (OR 0.27, 95% CI 0.24-0.31p &lt;0.001). Overall, the CPR between the two groups was significantly different: 44.69% in afterload ET and 41.65% in direct ET (OR 1.13, 95% CI 1.02-1.25, p = 0.017). As for the interaction between the two techniques and difficult transfer on CPR, only the direct difficult ET resulted in a significantly lower CPR with an OR of 0.62 (95%CI 0.49-0.77, p &lt; 0.001). Lastly, among the 15 operators that performed the ETs, a range of difficult transfers from 3.8% to 45.4 % in the direct group and 0.8% to 20.5% in the afterload group was found (p &lt; 0.001).

Limitations, reasons for caution
The main limitations of the study are the difference in sample sizes between the two groups, the wide range of time considered, and the 15 operators included. A further possible reason is the high prevalence of difficult transfer, probably due to the broad definition we used.

Wider implications of the findings
The study points out how in embryo transfers the use of the afterload technique instead of the direct one significantly improves clinical pregnancy rate and easy transfer rate. Since there is a limited knowledge on the embryo transfer technique impact, our findings aim to increase the effectiveness of embryo transfers.

Trial registration number
NCT05364528.