A glance into the uterus during in vitro simulation of embryo transfer.

Background: The currently low implantation rate after embryo transfer (ET) is partially attributed to technical aspects, such as catheter type, catheter load, placement of catheter tip and physician skills.

Methods: Mock ET simulations were conducted with a transparent laboratory model of the uterine cavity. The catheter was loaded with alternating air and coloured liquid media. The transfer procedure was recorded by a digital video camcorder for later analysis. Different sequences of air and liquid volumes, as well as liquids of different viscosity were simulated.

Results: Injection of liquid with air into the uterus formed an air bubble which blocked the transport of the transferred liquid towards the fundus. The distribution of the transferred matter within the uterine cavity was determined by the composition of the liquid-air sequence and the viscosity ratio between the transferred liquid and the uterine fluid.

Conclusions: It is suggested that the catheter load should contain minimal volumes of air in order to enhance the embryos' chances of reaching the site of implantation. The viscosity of the transferred liquid should be as close as possible to that of the uterine fluid in order to avoid transport of embryos towards the cervix.