An embryo transfer catheter with a protective sheath is disclosed. The use of a protective sheath shields a guide catheter from cervical mucus. The retracted open flaps of the outer protective sheath draw the mucus and blood away from the inner guide catheter. This allows an inner embryo transfer sheath to enter the uterus unobstructed. The embryo is then transferred to the uterus by means of fluid pressure with a culture medium. The protective sheath may be snap fit onto the guide catheter. The sheaths and catheters may be manufactured in a variety of lengths for individual convenience and then snap-fit onto each other for better control during an embryo implantation procedure. Other catheters and related instruments may also be manufactured with snap-on features.