Chilbirth (also called labour, birth, partus or parturition) is the culmination of a human pregnancy or gestation period with the delivery of one or more newborn infants from a woman's uterus. The process of human childbirth is categorized in 3 stages of labour. The first stage accomplishes the shortening and then the dilation of the cervix. It is deemed to have started when the cervix is 3 cm dilated, and ends with full dilation. Contractions begin in the first stage of labour although they may be irregular and sporadic at first. The second stage, often called the pushing stage, starts when the cervix is fully dilated and ends with the expulsion of the fetus. In the third stage, the placenta detaches from the uterine wall and is expelled through the birth canal. Preceding the onset of labour is a period called the latent phase. This phase may last many days, and the contractions are an intensification of the Braxton Hicks contractions that start around 26 weeks gestation. Latent phase ends with the onset of active first stage labour.