The uterus is a hollow, pear-shaped organ in a woman's lower abdomen in which a fetus grows during pregnancy. When a woman is not pregnant, her monthly menstrual period flows from the uterus.

The lower part of the uterus (cervix) opens into the vagina. The opening to the cervix is narrow except during labor and birth, when it stretches and widens to accommodate the baby's passage out of the uterus.