Background: Embryo transfer is a crucial step in the IVF process. Most randomized prospective studies comparing transfer catheters have demonstrated significantly higher pregnancy rates with soft versus firm catheters, but none have taken the operator effect into account. Our aim was to perform a prospective randomized clinical trial comparing two catheters and to study interactions between catheters and operators.
Methods: A prospective randomized trial comparing the Cook K-SOFT-5100 and Frydman classical catheters 4.5 was performed. Three experienced operators participated in the trial, using a fixed distance transfer protocol. Primary end-point was clinical pregnancy rate, secondary end-points were rates of difficult transfer and of catheter failure. Patients were randomized by a computer program prior to embryo transfer.
Results: A total of 1446 embryo transfers were performed in 1155 women undergoing IVF or ICSI treatment. A total of 723 cycles were randomized to the Cook catheter and 723 cycles to the Frydman catheter. Following intention-to-treat analysis, the adjusted odds ratio of clinical pregnancy between for the Cook versus the Frydman catheter was 1.11 [95% confidence interval (95% CI) 0.89-1.38]. Odds ratios of clinical pregnancy between the Cook and Frydman catheters for the three operators were respectively 1.19 (95% CI 0.84-1.69), 2.35 (95% CI 1.40-3.95) and 0.69 (95% CI 0.48-0.99).
Conclusions: Variation in pregnancy rates between embryo transfer catheters depends on variation between operators. Results from randomized clinical trials comparing embryo transfer catheters should not be generalized, because inconsistent conclusions may be unavoidable on the account of different proportions of cycles with transfers by each type of operator. The study was registered at clinicaltrials.gov. NCT00766714.