The myometrium's the middle layer of the uterine wall consisting of smooth muscle cells and supporting stromal and vascular tissue. The inner layer of the uterine wall's the endometrium or uterine lining, and the outer layer the serosa or perimetrium. The myometrium stretches (the smooth muscle cells expand in both size and number) during pregnancy to allow for the harboring of the pregnancy, and contracts in a coordinated fashion during the process of labor. After delivery the myometrium cont… (More on Myometrium)