To determine whether transvaginal ultrasound-guided embryo transfer is a technique that can be used routinely, whether it improves IVF outcomes and whether it makes difficult transfers easier and more successful.

Non-randomized retrospective study conducted between 2012 and 2016 in the fertility center of the Diaconesses-Croix St-Simon hospital group. The outcomes of 3910 transfers, performed by 5 senior operators, under transabdominal ultrasound guidance are compared with those of 800 transfers, performed by 1 senior operator under transvaginal ultrasound guidance. The criteria studied are the feasibility of the technique and the percentage of pregnancies per transfer in the two populations described, as well as in the difficult and very difficult transfer populations.

All the transfers were feasible under transvaginal ultrasound guidance without the use of forceps or additional instruments. The percentage of pregnancies per transfer is significantly increased, when the transfer is performed under transvaginal ultrasound guidance compared with that performed under transabdominal ultrasound guidance, in the general population (38%, n=800 vs 30%, n=3910; P 0.0004) and in the reference population characterized by age <38 years and >6 oocytes collected per puncture (45%, n=490 vs 36%, n=1968; P 0.002). The percentage of pregnancies per transfer (P/T) is not significantly different in the populations of easy transfers (n 695, 38% P/T), difficult transfers (n 58, 46% P/T; P=ns) and very difficult transfers (n 47, 34% P/T; P=ns).

Embryo transfer is a key stage in IVF, in which the quality of performance determines the outcome. In this study, transvaginal ultrasound guidance of the transfer, which is the reference procedure in gynaecological imaging, significantly increases the percentage of pregnancies per transfer, both in the general population and in the reference population, compared with transfers performed under transabdominal ultrasound guidance. Transvaginal ultrasound facilitates the performance of difficult transfers and in particular achieves outcomes in these situations that are not significantly different from those of easy transfers. Visual monitoring of transcervical passage, which is rendered more precise and less traumatic and precision of embryo deposition are the factors that probably account for the improvement in outcomes.