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Labor and Birth

Labor and Birth

Author: Amanda Soderlind

Understand the process of childbirth.

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Source: Video and Images Created by Amanda Soderlind

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Welcome to this lesson today on labor and birth. Today we will be discussing the processes and hormones involved in labor and birth. So birth will occur at 39 weeks approximately after fertilization. So the gestational period of humans is about 39 weeks. And hormones are actually involved in triggering birth once that time is up, once it's been about 39 weeks.

So hormones are secreted by the fetus, which will then trigger the placenta to produce more estrogen. So estrogen is one hormone involved in triggering birth. So fetus is triggering the placenta to secrete more estrogen. And then the increase in estrogen will trigger the release of oxytocin and prostaglandins, which will then stimulate the uterus to contract. So these are the three hormones that are involved in triggering birth.

So there are actually three stages to labor. And we're going to be discussing what happens in each of those stages of labor. So the first stage of labor occurs when the contractions of the uterus push the fetus against the cervix. So the fetus pushes against cervix.

Also during this stage of labor the cervix will dilate. And the amniotic sac will rupture. And we often refer to this as the water breaking. So contractions push the fetus against the cervix, the cervix will dilate, and the water will break.

Stage two of labor is actually the stage of labor where birth occurs. So stage two is birth. So during this stage, the cervix will continue to dilate until it reaches 10 centimeters. Once it reaches 10 centimeters, the baby is then ready to be born.

So contractions and the pushing of the mother will move the baby through the vaginal canal, usually head first. But occasionally, a baby will come out backwards, feet first, which we call breach. Now if the baby is positioned to come out feet first, the doctor must then turn the baby around to avoid any complications during birth. So if it's coming out the wrong way of it it's positioned opposite of head first, we refer to it as being breach. So the second stage of labor actually involves the birth of the baby.

And then the third stage of labor comes after the birth of the baby. So what happens at this point is that contractions of the uterus will force the placenta, fluid, and blood out. And we refer to this as the afterbirth. So this is when the placenta, fluid, and blood are forced out of the uterus.

At this point then, the umbilical cord can also be cut. And carbon dioxide will start to build up in the baby's blood. So while it was in the uterus, the placenta did the job of removing carbon dioxide from the baby's blood and replacing it with oxygen.

But since the placenta and the umbilical cord are no longer attached to the baby, carbon dioxide will build up in the blood. And that will force the baby to take its first breath. So temporary bypass vessels in the heart will at that point close, because they're no longer needed, along with the fetal heart opening. So at this point, the baby can now survive independently on its own. So gas exchange is now taking place in its lungs and it can survive independently.

So lactation is actually controlled by hormones as well. So after the baby is born, the mother will begin to lactate as controlled by these hormones here. So prolactin, oxytocin, estrogen, and progesterone are all involved in lactation. So lactation is milk production, milk production by the mammary glands in the mother's breast tissue.

So prolactin will stimulate milk production. Oxytocin causes the breast tissue to contract. And what that does is it pushes the milk into the ducts. And estrogen and progesterone are involved with the growth of the mammary glands and ducts. So these four hormones together play a role in milk production in the woman.

So this lesson has been an overview on the processes that occur during labor and birth, and the hormones that are involved with them.

Terms to Know

Occurs after the baby is expelled from the uterus, afterbirth is when the placenta separates from the uterine wall and is expelled from the mother.


When the fetus positions itself feet-first instead of head-first during labor.


The primary female sex hormone, estrogen promotes the development and maintenance of the female secondary sex characteristics; estrogen also plays a major role in the female making adjustments to pregnancy.


The secretion of milk from the mammary glands, hormonally stimulated by oxytocin.


A hormone secreted from the posterior pituitary gland (neurohypophysis) via a positive feedback mechanism once the child begins to put pressure on the cervix of the uterus.


A group of lipid-based chemical messengers in the body, prostaglandins during labor promote uterine contractions.