How does an embryo transfer work? The physician will insert a flexible trial catheter (which is inside a plastic sheath or sleeve) through the cervix and into the uterus. Once the tip of the catheter is in view in the uterus on the ultrasound monitor, the physician will remove the catheter but will keep the plastic sheath in place. This creates a clear “tunnel” for the catheter that will contain the embryo. The embryologist will load the embryo into a new flexible catheter and will bring that ca