Childbirth includes both labor (the process of birth) and delivery (the birth itself); it refers to the entire process as an infant makes its way from the womb down the birth canal to the outside world. The average length of labor is about 14 hours for a first pregnancy and about eight hours in subsequent pregnancies. However, many women experience a much longer or shorter labor.

Childbirth usually begins spontaneously, following about 280 days after conception, but it may be started by artificial means if the pregnancy continues past 42 weeks gestation. One of the first signs of approaching childbirth may be a "bloody show," the appearance of a small amount of blood-tinged mucus released from the cervix (the opening of the uterus) as it begins to dilate. This is called the "mucus plug." In about 10% of women, labor is signaled by the rupture of the amniotic sac. When a woman's...