The Three Stages of Labor: Dilation, Expulsion & Placental

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  • 0:05 Labor and Parturition
  • 1:34 The Stages of Labor
  • 2:20 The Dilation Stage
  • 5:11 The Expulsion Stage
  • 7:37 The Placental Stage
  • 8:48 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

You may think of the process of labor and childbirth as one long event, but it is actually divided into different stages. Learn about each of the three stages of labor in this lesson.

Labor and Parturition

Like many biological processes, the process of labor and delivery is divided into stages. The goal of the labor process is parturition, or the forcible expulsion of the fetus from the mother's uterus.

This process is accomplished through the use of contractions. Now, I know you're all probably familiar with the term contraction. You know, your muscles contract and relax as you move, right? Well, did you know that the contractions talked about during labor are similar to the muscle contractions that occur while you are walking, running, or just going about everyday actions?

But, there is one big difference. The muscles you use to move your legs and arms are voluntary and, for the most part, under your control. But, the uterus is made up of a certain type of muscle called a smooth muscle. This muscle is involuntary, meaning the mother cannot control the contractions of the uterus.

During true labor, contractions of the smooth muscles start at the top of the uterus and move downward, toward the cervix, in regular intervals. This is not to be confused with something called false labor, where the uterus contracts, but these contractions are irregular and do not aid in parturition.

The Stages of Labor

Okay, so now that we know the general method the uterus uses to accomplish parturition (that would be those contractions we just talked about), let's talk about the stages of the labor process. There are three of these stages:

  1. The dilation stage: this begins when true labor starts.
  2. The expulsion stage, which ends in parturition, or the birth of the baby.
  3. The placental stage, which, as you may be able to guess, is the expulsion of the placenta from the uterus.

Sounds pretty simple right? So, now that you know the general process of labor, let's look at each stage in a little more detail.

The Dilation Stage

First up: the dilation stage. The key player in this stage is the cervix. That's this part right here:

The cervix is outlined in red.

You may notice that the head of the baby is quite large compared to the tiny opening of the cervix. That's because this cervix hasn't dilated yet. Cervical dilation is the opening and widening of the cervix, providing an exit path for the baby. Amazingly enough, the cervix dilates to a width of ten centimeters during the dilation stage! This process can take hours to occur and is accompanied by a thinning of the cervical tissue as it dilates.

In the beginning, uterine contractions are occurring once every ten to 30 minutes, and they last for about 30 seconds each time, depending on how far along the mother is, of course. As the cervix continues to get closer to its fully open size of ten centimeters, the timing between contractions decreases.

For example, at the beginning of the dilation stage, when the cervix is only at about one to two centimeters, contractions may occur once every 30 minutes. But, as the cervix gets wider, contractions might begin to occur once every 20 minutes, and then once every ten minutes. As the dilation of the cervix reaches ten centimeters, the length between the contractions decreases.

Late in the dilation stage, the amniochorionic membrane inside the mother's uterus, which is a sac that contains amniotic fluid, may break or rupture. This is referred to as having one's 'water break' because the fluid is clear and, once the sac is ruptured, will leak out of the uterus through the open cervix.

Amniotic fluid is what helps insulate and protect the growing baby while in the uterus. It also helps prevent infection. So, if your - or your wife's - water (or amniotic fluid) breaks too early, the baby is then at risk of infection. In these special cases, the mother may be given antibiotics to help prevent infection, or she may go into early (or premature) labor.

But, under normal circumstances, a woman's water breaks toward the end of the dilation stage. When this happens, or if contractions start to come every five minutes or less, is it recommended that the mother get to the hospital as soon as possible because from here on out she will enter the next stage of labor.

The Expulsion Phase

The correct position of the baby for expulsion
Correct Expulsion Position

In contrast to the dilation stage, which can last hours, the expulsion stage usually takes less than one to two hours. It begins as the cervix completes its dilation and is pushed open by the head of the fetus. During the expulsion stage, contractions reach maximum intensity and propel the fetus out of the uterus, through the cervix, and down the birth canal.

Delivery, or birth of the fetus, is the arrival of the fetus into the outside world. At this point, our fetus is now called a baby or a newborn.

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