Parturition, also known as childbirth, is the act of giving birth to a baby. Parturition usually occurs about 280 days after a baby has been conceived. During the last three months of pregnancy the baby turns inside the uterus, or womb, so that its head lies against the cervix, or opening of the uterus. When parturition occurs, the baby is expelled by rhythmic contractions that take place in the muscles in the wall of the uterus. This process is called labor.
Labor takes place in three stages. In the first stage the cervix gradually opens so that the baby can pass through it. In the second stage the baby leaves the uterus and is born. In the third stage the afterbirth is expelled from the uterus. The afterbirth consists chiefly of the placenta, the organ through which the baby receives food and oxygen and gets rid of its waste products while it is in the uterus. The process of giving birth for the first time usually takes 12 to 18 hours, from the first labor pains to the expulsion of the afterbirth. Subsequent births usually do not take more than 10 or 12 hours. There is considerable variation, however, and in some cases, labor may last 24 or even 48 hours.
The first signs of labor are slight, brief cramps, which occur irregularly every 15 to 30 minutes. Gradually the cramps become stronger and occur closer together until they occur about every 3 minutes. During this stage the contractions of the uterus press the baby's head against the cervix, forcing the cervix gradually to dilate, or open. As the cramps become more intense, they may be quite painful. To help the mother over the uncomfortable parts of parturition, she may be given drugs or anesthetics.
The second stage of labor is the actual birth of the baby. In this stage, which is called delivery, the baby is pushed out of the uterus, through the birth canal, and into the world. As the contractions of the uterus continue, the baby's head begins to pass through the cervix. If the fluid-filled sac in which the baby has lived for the past nine months has not already ruptured, it now bursts, and the fluid escapes. This is commonly called the breaking of the bag of waters.
During the second stage of labor the mother helps expel the baby from the uterus and through the birth canal. As each contraction occurs, she pushes downward with the muscles of her diaphragm and abdomen. Finally, the baby's head passes through the birth canal. Once the head is through the cervix, the baby's shoulders, body, and legs usually emerge fairly easily and rapidly.
After the delivery the doctor holds the baby upside down to remove any secretions in the respiratory passages that might interfere with breathing. Most babies begin to breathe of their own accord. However, if the baby does not breathe spontaneously, the doctor stimulates breathing by stroking or slapping the baby's back. The doctor then cuts the umbilical cord, which connects the child to the placenta. The tiny stump of the umbilical cord that is left on the baby's abdomen dries up and spontaneously falls off, leaving at its base the navel, or belly button.
A few minutes after the baby has been born, the afterbirth is expelled from the uterus. Parturition is then complete.
Most births take place without complications. Occasionally, however, labor may not take place normally, or there may be some mechanical interference with the passage of the baby through the birth canal. For example, the baby may not turn into the usual head-down position in the uterus in the last three months of pregnancy, or its head may be too large to pass through the cervix. In such cases, a cesarean section may be performed.