Embryo Implantation in the Endometrium
The endometrium is the name for the mucous membrane constituting the inner layer of the uterine wall, also commonly described as the lining of the womb. Its structure, thickness and state change significantly through the menstrual cycle and its significance to fertility is that this is where the blastocyst will implant if a pregnancy is to progress. In fact “implantation” is a gentle way to describe the process. The ovum (egg) is sometimes described as behaving similarly to a parasite as it adheres to the endometrium. It destroys the epithelium at the point of contact and excavates a cavity into which it imbeds itself after which the endometrium closes over the damaged area. The part of the ovum which causes the damage to the endometrium is called the trophoblast but it doesn’t stop there. It actually absorbs the damaged part of the endometrium, grows over the entire ovum and penetrates into the maternal blood vessels. It continues growing and absorbing and in due course converts the endometrium into the placenta. Fertility doctors have tried to improve implantation rates by inserting embryos under the surface of the endometrium. However this has been found not to have any advantages over the standard practice of placing the embryo in the uterus and letting it “choose” where to implant itself.