Where does the blastocyst normally implant?

B. The blastocyst implants in the functional layer of the uterine endometrium. The uterus is composed of the perimetrium, myometrium, and endometrium. Two layers are identi-fied within the endometrium: (1) the functional layer, which is sloughed off at menstrua-tion, and (2) the basal layer, which is retained at menstruation and serves as the source of regeneration of the functional layer. During the progestational phase of the menstrual cycle, the functional layer undergoes dramatic changes; uterine glands enlarge and vascu-larity increases in preparation for blastocyst implantation.