The position of transfer air bubbles after embryo transfer is related to the pregnancy rate. With the conventional manual embryo-transfer technique it is not possible to predict the final position of the air bubbles. This position mainly depends on the catheter load speed at transfer (injection speed), a parameter that remains uncontrollable with the conventional technique even after standardization of the protocol. Therefore, the development of an automated device that generates a standardized injection speed is desirable. This study aimed to examine the variation in injection speeds in manual embryo transfer and pump-regulated embryo transfer (PRET). Seven laboratory technicians were asked to perform simulated transfers using the conventional embryo-transfer technique. Their injection speeds were compared with that of a PRET device. The results indicate that in manually performed transfers, even after standardization of the protocol, there is still a large variation in injection speed, while a PRET device generates a reliable and reproducible injection speed and therefore brings new possibilities for further standardization of the embryo-transfer procedure. Future research should reveal whether these experiments mimic real clinical circumstances and if a standardized injection speed results in more exact positioning of the transferred embryos and therefore higher pregnancy rates.

Background/Aims: Catheter injection speed affects depth and placement of the embryo into the uterine cavity and is shown to be highly variable in, and between, subjects in a manually performed embryo transfer. In an effort to standardize the injection speed during embryo transfer, we developed an automated transfer pump: the pump-regulated embryo transfer (PRET) device. In this randomized controlled trial, we aimed to investigate if standardization of the injection speed and pressure with this PRET results in a better controlled positioning of the transferred embryo(s). Methods: Five hundred ninety-nine in-vitro fertilization/intracytoplasmic sperm injection/frozen-thawed embryo transfer cycles were randomly assigned to the PRET or manual transfer. Positioning of the embryo(s) into the uterine cavity was measured with ultrasound. Results: The PRET device generates a significantly smaller variance of the positioning of the embryo(s) into the uterine cavity. This resulted in an ongoing pregnancy rate of 21% in the PRET versus 17% in the manual (p = 0.22) transfer group; frozen-thawed embryo transfers resulted in 17.5 versus 10.9% (p = 0.097), respectively. Conclusion: The PRET results in better controlled positioning of the embryo(s), and it also gives the opportunity to standardize embryo transfer. Whether the PRET may positively influence pregnancy rates, needs to be investigated in a multicenter trial.