Parturition, also called childbirth or birth, is the process of bringing forth an infant from the uterus (the womb).

This process can be divided into three stages:

• first stage: dilation;
• second stage: expulsion; and
• third stage: placental stage.

Your part in the delivery process will be given in detail in Lesson 2 of this subcourse. This brief description of the three stages will allow you to become familiar with the anatomy of pregnancy and delivery.

a. First Stage: Dilation.

(1) In this stage, the cervix opens up (dilates) to a diameter of 10 cm (4 inches). This opening is large enough for an infant’s head to pass through. At the beginning of this stage, the contractions of the uterus (labor) occur about every 20 to 30 minutes and last for about 40 seconds. Contractions take place about every three minutes until the cervix is fully dilated to 10 cm.

(2) The length of time it takes for a woman’s cervix to dilate completely varies greatly. Usually, full dilation takes longer in a woman having her first baby– perhaps 14 hours. At the other extreme, a woman who has had several children may be fully dilated in less than an hour. Even these estimates are not always true. Do not count on a woman having a long period of dilation just because she is having her first child. About the time the cervix becomes fully dilated, the amniotic sac breaks. The contractions of the uterus force the amniotic sac down toward the cervix. The pressure on the sac causes it to burst, spilling its contents out (breaking of the bag of waters).

b. Second Stage: Expulsion. The child is actually delivered at the end of this stage. During the expulsion stage, the baby is pushed through the birth canal. If themdelivery is normal, the crown of the baby’s head emerges first. Then the shoulders emerge, one shoulder at a time. The lower part of the baby slides out quickly after the shoulders emerge. The average time of this stage of childbirth is one hour and 45 minutes.

c. Third Stage: Placental Stage. The uterus becomes much smaller when the child is delivered. As the uterus becomes smaller, the placenta (afterbirth) becomes detached in several places from the lining of the uterus. A few minutes after childbirth, uterine contractions force the afterbirth into the vagina from which the placenta is expelled. Expect some bleeding. A normal amount is one to two cups of blood. Sometimes there is a delay in the separation of the placenta from the uterine lining, and there is more than a normal amount of bleeding. When this occurs, the bleeding must be controlled, and the afterbirth may need to be removed artificially.