Received July 27, 2015
Accepted September 23, 2015

Objective: This study aimed to compare the use of semi-rigid and flexible catheters in terms of pregnancy rate and level of difficulty of the embryo transfer (ET) procedure. Methods: Seven hundred and thirty-nine consecutive follicular aspirations for IVF or ICSI performed in our private fertility clinic within a 30-month period were randomly divided into two groups. Patients were allocated to either of the groups at the time of follicular retrieval with the aid of a random number generator according to the catheter used in ET: Group 1 (n = 370) – Frydman Classic Catheter 4.5 catheters; and Group 2 (n = 369) – Frydman Ultrasoft 4.5 catheters. Only patients offered ET in the randomized cycle were included (Group 1 = 363 and Group 2 = 340). Patients did not change groups after catheter allocation.Statistical analysis was carried out using an unpaired t-test or a chi square test as appropriate. Differences with P<0.05 were considered. Results: A statistically significant difference in favor of the use of the Ultrasoft catheter was evident for parameters use of a tenaculum (19.8% vs. 5.9%) or a hysterometer (5.0% vs. 1.2%), presence of blood during post-ET inspection of the catheter (9.9% vs. 3.8%), and implantation rate (13.0% vs. 16.4%). Clinical pregnancy and delivery rates were comparable in both groups. Conclusions: Our results suggest that a softer catheter may help with difficult ETs. Softer catheters, as also reported by other authors, resulted in better implantation rates.