The |uterus|, or womb, in which the |fetus| grows is a thick-walled, hollow, pear-shaped organ, with two parts, the body above and the narrower |cervix| which protrudes into the |vagina| below. Its position in the female body is between the |bladder| and the |rectum|. During |pregnancy| the |uterus| expands as the |fetus| grows, increasing thirtyfold by full term. Uterine |contractions| are usually the beginning of the labor process. When the |uterus| starts contracting, it presses the amniotic sac into the |cervix|, which ruptures the sac. In the second stage of labor the uterine |contractions| become more severe and are aided by the |contraction| of the abdominal muscles in propelling the |fetus| through the |vagina|. After delivery the |uterus| contracts in volume and slowly shrinks.
