The uterus is categorized as anterior, flat, or posterior based on the relationship of the longitudinal axis of the uterine body to the longitudinal axis of the body. The posterior position of the uterus is the direction of the uterine body towards the sacrum. The uterus is divided into the cervix and the body of the uterus, and if the longitudinal axis of the body of the uterus is parallel to the longitudinal axis of the body, it is in the flat position. An analogy is that the uterus is like a person standing up in the abdominal cavity; if it is standing straight it is flat; if the uterine body is directed toward the pubic bone, like a person bowing, it is an anterior uterine position; and if the uterine body is directed toward the sacrum, like a person standing and leaning back, it is a posterior uterine position. The position of the uterus is generally more anterior, but the posterior position does not affect the physiologic role of the uterus. Some women are prone to the sleepy feeling of soreness in the lower back because the posterior uterus irritates the pelvic peritoneum.