Natural childbirth IV: the hormones of birth

August 3, 2011 in Fertility, Pregnancy & Childbirth | 6 comments

baby breastfeedingBefore we discuss how modern medical interventions like epidurals and synthetic oxytocin (Pitocin) can interfere with undisturbed birth, we need to understand the hormones of birth.

The natural regulation of hormone balance is an exceedingly sophisticated and complex process. And although we know the basics of how hormone regulation works, there is still much we don’t understand.

I’ve argued against using supplemental hormones to as a first step in treating hormone imbalances for exactly this reason. Whenever we take hormones, we run the risk of disrupting the delicate negative feedback system that regulates our own internal production of these hormones.

The image that comes to mind is a monkey in the cockpit of the space shuttle pushing a bunch of buttons.

Perhaps that’s an exaggeration, but the point is that any intervention that risks disrupting natural hormone balance and regulation is apt to cause problems. And there’s no time that’s more true than during pregnancy and childbirth.

The hormones of birth

The hormones of birth include estrogen and progesterone, oxytocin, beta-endorphins, prolactin and catecholamines (epinephrine/adrenaline and norepinephrine/noradrenaline).

Estrogen and progesterone

Estrogen and progesterone are the main hormones involved in “setting the scene” for birth, including activating, inhibiting and reorganizing other hormone systems. They both play a crucial role in the initiation of labor. For example, the placental production of estriol increases by more than 1,000 times close to the onset of labor, and progesterone production increases 10-18 times higher.

Estrogen has also been shown to increase the number of uterine oxytocin receptors and gap junctions in late pregnancy, which is thought to prepare the uterus for contractions in labor.


Oxytocin is the hormone associated with the contractions of labor and birth in all mammalian species. It has also been referred to as the hormone of love because of its involvement with sexual activity, orgasm, birth and breastfeeding.

In the context of undisturbed birth, Odent refers to oxytocin as the hormone of “forgetting oneself”.1 This is crucial because a fundamental aspect of an undisturbed birth is the sensation of an altered state of consciousness: “being transported” or “going to another world”.

Oxytocin is stored in the anterior pituitary and released in pulses every 3-5 minutes during early labor, becoming more frequent as labor progresses. Keep this in mind when we discuss the differences between natural oxytocin and synthetic oxytocin (Pitocin) used to induce labor in hospitals.

Current research suggests that oxytocin is the initiator of the rhythmic contractions of early labor, while prostaglandins produced locally in the uterus assume that role later in labor.

Some recent studies have found that oxytocin produced by the fetus may directly stimulate the mother’s uterine muscle, suggesting that the baby may be responsible for initiating labor.

Finally, oxytocin plays several important roles after birth. High levels of oxytocin produced as the baby stimulates the mother’s breast help keep the uterus contracted and prevent postpartum hemorrhage. Oxytocin mediates the “milk ejection reflex” which allows for successful breastfeeding. And, as the hormone of love, oxytocin promotes the development of a strong bond between mother and baby.


Beta-endorphin is a naturally occurring opiate that acts to restore homeostasis (internal balance). It is secreted by the pituitary gland in times of pain and stress. It activates the mesocorticolimbic dopamine reward system and produces pleasure in association with sex, birth and breastfeeding.

Studies suggest beta-endorphin increases tolerance to pain and suppresses the immune system, both of which are important during birth.

Beta-endorphin is similar to the addictive opiates morphine and heroin in that it induces feelings of pleasure, euphoria and dependency. Beta-endorphin levels during labor reach similar levels to those found in male endurance athletes during maximal exercise on a treadmill.

High levels of beta-endorphin help the mother to tolerate the pain of labor and nudge the her into the altered state of consciousness that characterizes an undisturbed birth. After the baby has been born, beta-endorphin (like oxytocin) reinforces the mother-infant bond and contributes to ecstatic feelings for both.

Finally, beta-endorphin promotes the release of prolactin during labor, which prepares the mother’s breast for lactation and aids in lung maturation for the baby.


Prolactin is known as the mothering hormone. It’s released by the pituitary during pregnancy and lactation, and it prepares a pregnant woman’s breasts for lactation.

During breastfeeding, prolactin levels influence sucking intensity, duration and frequency. Researchers believe prolactin (together with oxytocin) is responsible for the elevation of mood and feeling of calm mothers experience after breastfeeding.

Prolactin is also believed to play an important role in maternal behavior after birth via its effect on the nursing mother’s brain. It has been referred to as the hormone of “submission” or “surrender”. In the breastfeeding relationship, it may encourage the mother to put her baby’s needs before her own.

According to Sarah Buckley, M.D.2:

There are more than three hundred known bodily effects of prolactin, including induction of maternal behavior, increase in appetite and food intake, suppression of fertility, stimulation of motor and grooming activity, reduction of the stress response, stimulation of oxytocin secretion and opioid activity, alteration of the sleep-wake cycle and increase in REM sleep, reduction of body temperature, and pain relief. Prolactin, along with growth hormone, is one of the hormones of growth and lactation and as such has a crucial influence in the development and function of the immune system.

And those are just the functions we know about!

Catecholamines (CA)

These are the “fight or flight” hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). They’re produced in response to hunger, fear and cold as well as excitement.

During labor, maternal CA levels gradually rise, peaking right before transition (the contractions which finish dilating the cervix in the first stage of labor).

This tells us the stress hormones are an important part of a healthy birth. However, if a woman’s epinephrine levels are too high (reflecting activation of her “fight or flight” response) early in labor, uterine contractions will be inhibited and labor will be slowed or even stopped completely.

High levels of CA can stimulate uterine contractions, which contribute to what Michel Odent calls the “Fetus Ejection Reflex“. According to Odent this reflex occurs at transition and almost always follows an undisturbed birth, probably because CA levels must be low early in labor for it to happen optimally.

On the other hand, high levels of CA too early in labor (which would be triggered by activation of the woman’s “fight or flight” system in response to fear or perceived danger) have been shown to inhibit uterine contractions.

This is yet another example of the exquisite regulation of hormones by the body and the danger of interfering with this natural process. CA levels must be just right at all stages for an undisturbed birth. If the mother is afraid or feels she is threatened or in danger early on, labor will be inhibited. I suspect this happens fairly often in the hospital setting. On the other hand, if the natural increase of CA levels that should occur later in labor is blocked (by painkillers or other drugs), then the fetal ejection reflex will not be stimulated and delivery may be more difficult.

Now that we have a better understanding of the hormones involved in birth, we can move on to exploring how modern medical interventions disrupt the natural regulation of these hormones and interfere with “undisturbed birth”.

  1. Odent M. The scientification of love. Free Association Books 1999.
  2. Buckley S. Gentle birth, gentle mothering: a doctor’s guide to natural childbirth and early parenting choices. Celestial Arts 2009. pp.109

{ 6 comments… read them below or add one }

Becky August 3, 2011 at 12:06 pm

Chris—thank you for all you do! I am so grateful for the wealth of knowledge you share with your readers, especially this latest series regarding natural birth. I have learned so much and am so excited to begin my childbearing years with a better understanding of what is truly going in my body.

I do have a request, however. Would Elanne be willing to share her undisturbed birth experience with us? I understand if she would prefer not to share, but it would be great to hear her story and her feelings, thoughts, perceptions, advice, etc.

Again, thank you! —-Becky


Chris Kresser August 3, 2011 at 12:10 pm

I’ve asked Elanne to write a guest post doing just that, and she has agreed. However, it could be some time before that happens, for obvious reasons. In the meantime, I’ll talk a bit about my experience of the birth on the next podcast.


Allison Evans August 3, 2011 at 4:57 pm

Thank you for this excellent explanation of the hormones of labor. It reminds me a bit of nutrition, how we know a bit about it and think we know everything. The result is we eat poor foods but take a multivitamin and think we’re okay. The crude manipulations of labor interventions are — as you say — like putting a monkey at the controls of a sophisticated machine. I listened yesterday to a friend’s birth story. She had prepared for a natural birth, but once she got to the hospital her contractions slowed down. So she agreed to the “minimal” intervention of having her membranes ruptured. It completely changed her experience of labor from something “slow but comfortable” to extreme discomfort requiring an epidural. . . and then pitocin. I can’t wait to read your next post about hospitals!


Allison Evans August 3, 2011 at 4:58 pm

P.S. I would love to be able to repost your blogs onto facebook or e-mail them to my expecting parents. What can I do? Thanks!


Chris Kresser August 3, 2011 at 5:02 pm

Allison: at the top of every post there is a Facebook sharing icon. Just click on that and you can share the post to Facebook. As for email, just copy the link and paste it in an email.


Brooke August 4, 2011 at 11:07 pm

Beautifully and concisely written. I am so excited and encouraged by reading your articles Chris. Thank you so much for sharing your wealth of knowledge. I am a Registered Nurse and I work in a Neonatal Intensive Care environment.This past year through my research and reading your blog and posts I have been enlightened. I understand that what I do is valuable for critically ill infants. However I am so encouraged to hear that safe, natural childbirth is a reality and why it is a reality. The scientific background and research allows me to embrace it.
For some time I have wanted to go back to school and become an advanced practice nurse via a Master’s degree program. Through all this I have realized that my path is to become a certified nurse midwife and women’s nurse practitioner.
Looking forward to many more segments on the topic of natural childbirth. I can’t wait to hear about your’s and Elanne’s birth experience. Thank you.


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