The Hormones of Labour & Birth

Have you ever wondered why our pets seek out a quiet, dark, and private space to give birth? You might have noticed that your furry friend has chosen to burrow into your favourite dressing gown, prompting you to disturb them to save your cuddly, warm, and well-worn dressing gown from being covered in birthing remnants. Now that you’ve interrupted her, she scurries away. This makes you ponder and compare your birthing wishes with your fur child's labour and birth process.

Why do our pets seem to birth so easily, yet the process seems so difficult for us? Human babies are born the same way for all mammals, using the same hormones, which are the body’s chemical messengers. These hormones, which stem from the deepest and oldest parts of our brain, assist the physical processes of labour and birth and influence our behaviours and emotions.

If humans respected their origins as mammals more, the hormones they share at birth could be much more like those of other animals.

For labour and birth to function, the hormone oxytocin must be present. Oxytocin is the hormone responsible for love and bonding, and it also plays a critical role in breastfeeding for all mammals. It is needed in labour and birth for the uterus to contract and for boosting the production of prostaglandins, which help stimulate uterine contractions. As oxytocin levels rise, so does the strength of labour, triggered by pressure on the cervix as the baby moves down. Oxytocin also acts as a pain relief by activating the brain’s reward centres during labour and birth, which is commonly experienced as a sense of euphoria that mothers often feel during a physiological birth. When labour is progressing as expected, oxytocin levels will be sufficient, along with prostaglandins, to maintain consistent and strong contractions throughout labour. If your labour stalls or does not start by itself, you may be offered the synthetic hormone called Syntocinon to assist your uterus in contracting. It is important to note that Syntocinon is administered into a vein, not your brain, where natural oxytocin is released. This means that the same love, bonding, and pain relief effects seen with natural oxytocin are not present with artificial oxytocin. In fact, high doses of synthetic oxytocin over a prolonged period can reduce natural oxytocin sensitivity and increase the risks of postpartum haemorrhage.

For labour and birth to work, we also need a mixture of our stress hormones, known as catecholamines. Adrenaline and noradrenaline, commonly referred to as our ‘fight or flight’ hormones, are evoked with feelings of stress or excitement. When adrenaline is released, the body undergoes physical changes, such as the heart beating faster and the lungs functioning more efficiently. Blood is rapidly directed to the brain, arms, and legs, enabling the body to ‘flight’ if necessary. Blood pressure rises, and a heightened sensation of alertness becomes apparent as blood sugar levels rise to provide a burst of energy in case you need to ‘fight’.

The hormone adrenaline is very important during birth as it helps to promote the safety and security of the environment you are in and the safety within yourself. Adrenaline is continuously dispersed throughout labour, essential for the energy needed to birth your baby. Even if labour has started, certain factors can make labour stall or even stop altogether. Like animals, our mammalian bodies use the same hormones to postpone labour and seek safety if danger is sensed.

When a woman is early in her second stage of labour, when her cervix is fully dilated but without the need to push, she may feel a desire for rest. Suddenly, she may experience a burst of energy from high catecholamines levels. Combined with oxytocin, these hormones can help promote strong contractions, leading to involuntary pushing, often referred to as the ‘fetal ejection reflex’. These hormone levels drop quickly after birth, which can leave the mother feeling shaky or cold.

Another childbearing hormone needed for labour and birth is prolactin, which is required mainly after birth for breast milk synthesis. When the newborn begins suckling at the breast, prolactin increases. Early and frequent suckling assists the breast in being more responsive to prolactin, which is needed for a sufficient long-term milk supply.

Our final hormone essential for labour and birth is beta-endorphins. This hormone, released by the brain during times of stress or pain, has been found to be as effective as pain-relieving drugs like pethidine. It helps mothers feel as though they are not in the same world; they enter ‘labour land.’ However, the presence of actual medications for pain relief during labour can reduce the levels of this hormone. Another remarkable response from beta-endorphins is their ability to activate our learning and memory, which may explain our detailed recollections of labour and birth. Similar to oxytocin, endorphin hormones contribute to that euphoric feeling and are released during lovemaking and breastfeeding. Interestingly, endorphins are present in breastmilk, which accounts for the natural high that babies experience after breastfeeding. Additionally, beta-endorphins assist in the release of prolactin, highlighting the significant interplay of hormones involved in labour, birth, and breastfeeding.

Now, returning to your labouring cat: when you disturb your furry friend, it can cause feelings of fear, unsafety, and heightened alertness. This reaction triggers an overproduction of adrenaline and inhibits the release of oxytocin, ultimately stalling or even halting the progress of labour altogether. In humans, this phenomenon is commonly observed during the transfer from home to hospital in the early stages of labour. It presents as contractions that occur regularly at home and increase in intensity, but once in the hospital, these contractions may disappear or become more manageable due to peaks in adrenaline and noradrenaline, which inhibit oxytocin release. By disrupting the space your cat picked out to labour down in, you undermine their sense of safety, which can further stall labour.

All these hormones mentioned need to be working to produce a mammalian labour and birth process, but these aren’t all the hormones at play, working together to bring your baby safely into this world. We know that there are many other factors influencing birth that we are still trying to better understand.

Evidence shows that all mammals, whether human or animal, seek a safe place to give birth. This behaviour is known as our nesting instinct. To labour effectively, we must feel safe, calm, and private.