The uterus is a specialized muscular organ that provides an appropriate environment for the growth and development of the embryo and fetus, as well as protects it. It plays an essential role in the formation of the placenta, and at the time of delivery, its thick muscular wall contracts to help expel the fetus. In a non-pregnant adult, the uterus is said to resemble a small inverted pear. The main part is the body, with the uterine tubes entering it superiorly and laterally. The upper margin is known as the fundus, and the lower part tapers into the cervix, which opens into the vagina.
The uterus occupies a midline position in the pelvic cavity, separated from the bladder by the utero-vesical pouch and from the rectum by the recto-uterine pouch. Often, the body of the uterus is bent forward (anteflexed) with respect to the cervix, so that it rests on the bladder. During pregnancy, the uterus enlarges to accommodate the growing fetus, and can even rise as high as the xiphoid process.