Part I: Birth hormones—the quiet, unsung heroes
Updated: Jan 21
Feeling hormonal? Love ‘em or hate ‘em, at the day-to-day hormones are an essential part of having a body... but it’s a fine balance. Too much, too little, none, or misfires can send literal mixed messages to your brain, body, and organs leading to a whole slew of issues. Now WHEN they work? Magic (no, science). The role of hormones in pregnancy, labour, birth, and postpartum is pretty fascinating and tedious stuff. Yeah, yeah, yeah. I’m a birth nerd so it’s easy for me to say, but bear with me! Hormones can be hard to wrap your brain around, and they're not exactly a hot topic in the doctor’s office. There is also a host of NEW (2014ish) research on the what, when, why, and how of these hormones that has helped us better understand their mystique in recent years! If you want the whole kit and caboodle, the epic report Hormonal Physiology of Childbearing by Sarah J. Buckley is here. But I will be honest… it’s way more than you need to know. It’s way more than I need to know.
Let’s just start with a basic definition, shall we? What is a hormone? According to Collins dictionary, "a hormone is a chemical, usually occurring naturally in your body, that makes an organ of your body do something." That's a bit vague and broad. Think of them as little secret messages sent through your body with the instruction manual of how to do a certain thing. In this case, the map for how to give birth!
Some of the key things hormones accomplish in pregnancy?
· Help your uterus (and baby) grow together.
· Prepare breasts for milk-production.
· Relax your ligaments so your body can handle all that growth (and prepare it for birth). We’re going to focus on what they do in labour and birth though, because that song and dance is most impressive and deserves to be recognized (/understood) if it’s likely to happen to you. Some of the key things hormones accomplish in labour/birth?
· Strong, productive, uterine contractions.
· Protecting and preparing baby (during and after birth).
· Pain relief during labour and after birth.
· Bonding and caring instincts once baby arrives.
The main shining stars of labour and birth are:
· prolactin (“caregiving”/“mothering” hormone)
· oxytocin (“love”/"bonding" hormone)
· endorphins (“pain-relieving”/“pleasure” hormone)
· catecholamines (“fight-or-flight”/stress hormones)
Here’s a rundown of how the Fab Four work (together) to support physiologic birth!
During the final weeks of pregnancy, you’ve got some side-stage (but crucial) hormones that ramp up: relaxin, prostaglandins and estrogen. They help to soften, thin, and perhaps start to open the cervix to make labour efficient. When baby is ready and their lungs are fully mature (with the help of rising catecholamines/stress hormones), it is believed the baby releases prolactin. This message starts a domino effect of more hormone signals to start the process of labour.
The gradual rise in oxytocin during later pregnancy gets the ball rolling on contractions. Oxytocin produces and regulates uterine contractions in labour, making them more effective, efficient, and stronger as labour progresses. If baby is in the optimal cephalic (head-down) OA (occiput anterior) position, pressure on the cervix during contractions brings on both cervical dilation, further oxytocin signals, and thus, stronger contractions. Of course stronger contractions can feel more intense, so: enter endorphins! These natural opiates (similar to morphine/heroin) release and increase throughout labour in direct response to that increasing “pain” of productive, progressing, oxytocin-fueled contractions. They flood your pain-receptors with calm and relief so you can KEEP progressing. Sometimes people report getting into a zone or “labourland” if they are able to sink into their contractions with calm—that’s thanks to endorphins! It’s the same hormone responsible for a runner’s high, if you're familar with that feeling. I'm not, HA! Catecholamines and stress hormones are important, but not yet. If they (and/or cortisol, the “fight-or-flight” hormones) are over-released during the first stage of labour due to spikes in stress and feeling threatened (perceived or real), oxytocin production may slow or even stall labour contractions. In early humans, this was an appropriate and important response to threats to quickly seek out safer spaces to give birth. Low-levels of oxytocin during labour and birth may also increase the risk of postpartum hemorrhage. Your hormone-receptors do have limited space, so if stress hormones creep in it can override the oxytocin. We want to support the flow of oxytocin (and the helpful endorphin response) by fostering as relaxing, safe, calm, and supportive an environment as possible to keep stress hormones low. Stress hormones can also cause distress to baby, triggering abnormal fetal heart rate readings.
However, during the second stage of labour (pushing), small bursts of catecholamines can give a needed boost of energy and clear-headedness that help you to push effectively. Further surges of catecholamines can trigger the “fetal ejection reflex,” where the birthing person might spontaneously bear down without any conscious effort. The catecholamines pass through the placenta to enter the baby’s system, keeping them alert immediately after birth and helping their lungs take their first breaths of air. Oxytocin peaks during second stage as well, working in tandem with catecholamines to further support spontaneous pushing (“Ferguson reflex”).
Once baby arrives, those oxytocin contractions continue to help expel the placenta, limit bleeding, and gradually shrink the uterus to its pre-pregnancy size by the process of involution. Oxytocin also promotes breastfeeding and bonding behaviour after birth, and produces the "let-down" or "milk-ejection reflex" required for breast/chestfeeding. Endorphin surges at birth cause you to feel alert and perhaps numb (or blissfully unaware) to the pain, and contribute to feelings of bonding and euphoria. Just as labour began with prolactin, it surges again the end of labour to help pace the last stage, promote caregiving/nurturing behaviours, the regulation of baby’s body temperature, and milk-production after birth.
So there you have it! Teamwork makes the dream work! Part II can be found here to find out all about what you can do to encourage, protect, and support the hormonal/physiologic processes of birth—as best as possible, of course.
Buckley S. 2015. Hormonal Physiology of Childbearing: Evidence and Implications for Women, Babies and Maternity Care. Childbirth Connection, Washington, DC.