|Childbirth| is referred to as labor and parturition, and it occurs in three stages. The first stage starts with uterine |contractions|, which press the amniotic sac into the |cervix| where it is ruptured. The amniotic fluid lubricates the cervical canal, facilitating the passage of the head of the |fetus| through the cervical canal. In the second stage of labor the uterine |contractions| become more severe. The abdominal muscles contract and aid in propelling the |fetus| through the |vagina|. The birth of the baby occurs in this stage. At this point the |umbilical cord| is still attached and needs to be severed. After the birth of the infant the |placenta|, or afterbirth, is expelled in the third stage. A full-term |pregnancy| is usually regarded as one which ends in delivery anywhere between 38 and 42 weeks.
