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 near the end 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 the
delivery 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
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
more than the normal amount of bleeding occurs. When this happens, the bleeding
must be controlled and the afterbirth may need to be removed artificially.