labium

Definition labour

labourl: labour n. the sequence of action by which a baby and the afterbirth are expelled from the womb at childbirth. The process usually atars spontaneously about 280 days after conception, but it may be started by artificial means (see induction). In the first stage the muscular wall of the womb begins contracting while the muscle fibres of the cervix (neck of the womb) relax so that the cervix expands. A portion of the membranous sac (amnion) surrounding the baby is pushed into the opening and bursts under the pressure, releasing *amniotic fluid to the exterior. In the second stage the baby's head appears at the cervix and contractions of the womb strengthen. The passage of the infant through the vagina is assisted by contractions of the abdominal muscles and conscious pushing by the mother. When the top of the baby's head appears at the vaginal opening the whole infant is eased clear of the vagina, and the umbilical cord is cut. If the emergence of the head is impeded a cut may be made in the surrounding tissue (see episiotomy). In the final stage the placenta and membranes are pushed out by the continuing contraction of the womb, which eventually returns to its unexpanded state. The average duration of labour is about 13 hours in first pregnancies and about 8 hours in subsequent pregnancies. Labour pains can be lessoned by previous training of the abdominal muscles and by the use of drugs. See also Caesarian section.