Childbirth, labor, birth, partus, or parturition is the culmination of a human pregnancy or gestation period with the expulsion of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and birth of the infant, and birth of the placenta. In many cases, with increasing frequency, childbirth is achieved through caesarean section, the removal of the neonate through a surgical incision in the abdomen, rather than through vaginal birth. In the U.S. and Canada it represents nearly 1 in 3 (31.8%) of all childbirths. More than 22% of women undergo induction of labor and childbirth in the United States, doubling the rate in 2006 from 1990.