Oxytocin and birth: the latest evidence

So what is oxytocin?

When thinking about the notion of drug abuse, I’m guessing that most people’s minds would initially conjure up images of cannabis, heroin, methamphetamine or cocaine; drugs used on the street, illegally, and in ways often viewed as problematic. 

But of course these and other so-called street drugs have the very same pharmacological roots as some of the drugs used in medicine. In a medical context, however, similar substances are legal and their use is controlled by professionals. They are viewed as therapeutic, and good.

I realise that most readers will already be aware that the cultural context in which a drug is used changes the way it is viewed. A degree of legitimacy is conferred where the drug is administered in a professional context. But some of the substances used in childbirth are also highly problematic when looked at more closely.

For example, there is increasing concern about the use of one particular substance used in maternity settings – oxytocin, which is also known as Syntocinon or Pitocin – and in this blog post I highlight some of the reasons for this concern, and share some of the research that has been carried out over the years.

What is oxytocin used for?

Millions of women and babies are exposed to exogenous oxytocin during labour, because this is given to induce and augment (speed up) labour, as well as in medically managed placental birth and to stop bleeding after birth.

There is no doubt that it can save lives, especially when used to treat postpartum haemorrhage, but there is also no doubt that it carries risks.  

Oxytocin has long been listed as a high-alert medication by the US-based Institute for Safe Medication Practices (e.g. ISMP 2014), which means that it has been identified as posing a significant risk of harm when used in error, and has also frequently been cited in legal cases as being associated with a range of adverse outcomes (Jonsson et al 2007).

Oxytocin-related research

Studies have been highlighting problems with the use of oxytocin for many years.

For instance, the authors of a Cochrane review of high versus low dose oxytocin wrote that:

“Whilst high doses [of oxytocin] cause contractions to occur sooner they can cause hyperstimulation or sustained contractions that can impair blood flow to the placenta and hence cause fetal distress. Further adverse effects of high total doses of oxytocin include hypotension with reflex tachycardia, water retention, and hyponatraemia (Rang 2007).” Budden et al (2014).

In another systematic review, Begley at al (2014) found that oxytocin was associated with adverse neonatal outcome and operative delivery, and encouraged the use of positive, health-focused outcomes in future work. 

Elsewhere, Bernitz et al’s (2014) recent research in low-risk nulliparous women without dystocia found an association between the use of oxytocin and an increased chance of instrumental vaginal birth and episiotomy. 

Other side effects often reported by women include headache, nausea, vomiting, arrhythmia, bleeding, skin rashes, uterine rupture, increased risk of clotting and increased risk of urinary incontinence (Wickham 2018).

More oxytocin-induced problems

The work of researchers such as Kirsten Uvnäs Moberg (2003) expanded our knowledge of the positive effects of natural oxytocin in pregnancy, birth, breastfeeding and many other areas of life, while books like those written by Sarah Buckley (2005) have helped spread knowledge about how synthetic oxytocin given during labour reduces the number of oxytocin receptors and thus desensitises the woman’s uterus to the effects of her own oxytocin. 

This unwanted side effect has many negative implications which we are only beginning to understand. Other alleged problems, often discussed by professionals but more indirect and thus less easy to quantify in research studies are that the overuse of oxytocin as an induction agent has led to many babies accidentally being born prematurely, which then involves needless admissions to special care units. 

It is also vital to look at women’s experiences of synthetic oxytocin. 

In one study, Bergqvist et al (2012) looked at the experiences of women who had slow labour progress with their first babies, comparing those who received early oxytocin to women who had augmentation postponed. Almost one in three women in both groups had negative and depressing memories of their birth, and operative births were associated with significantly worse childbirth experiences. 

The authors concluded that, “Early oxytocin augmentation for slow labour progress does not appear to be more beneficial than expectant management regarding women’s perceptions of childbirth one month postpartum. Given the risks for the foetus associated with oxytocin treatment, prudent expectant management seems to be a safe and viable alternative.” (Bergqvist et al 2012: 61). 

We need more of this kind of research.

Weighing the risks and benefits

I’m not saying that synthetic oxytocin is all bad.  Used appropriately, it can be very useful, and of course there are situations where the benefits will be considered to outweigh the risks. 

But the frequency with which this drug is currently used may not be justified, and the risks and implications of its use have caught the attention of researchers in a number of fields. 

A systematic review

The authors of a 2023 systematic review found that:

“Synthetic oxytocin infusion during labour increased maternal plasma oxytocin levels 2–3-fold at the highest doses and was not associated with neonatal plasma oxytocin elevations.

Therefore, direct effects from synthetic oxytocin transfer to maternal brain or fetus are unlikely.” (Buckley et al 2023).

As one of the researchers clarified for me when we were discussing the paper, this means they think that it is unlikely that autism is caused by Syntocinon use.

“However, infusions of synthetic oxytocin in labour change uterine contraction patterns. This may influence uterine blood flow and maternal autonomic nervous system activity, potentially harming the fetus and increasing maternal pain and stress.” (Buckley et al 2023).

It’s also possible that some of the effects that we see, for instance in breastfeeding and mental health, may occur in an indirect rather than a direct manner.

People often talk about synthetic oxytocin. But it’s important to understand that the oxytocin given is the same molecule as the body’s own oxytocin from a pharmacological perspective. Dr Kerstin Uvnäs-Moberg talks about this in her work. But the effects on the body are different depending on whether it is secreted within and by the body itself (endogenous oxytocin) or administered into the body by via drip, nasal spray or other external method (exogenous oxytocin.)

Hormonal Physiology of Childbearing

One of the best resources to help you understand the science around the hormones of birth is Hormonal Physiology of Childbearing: Evidence and Implications for Women, Babies, and Maternity Care.

“Overall, consistent and coherent evidence from physiologic understandings and human and animal studies finds that that the innate, hormonal physiology of mothers and babies—when promoted, supported, and protected—has significant benefits for both in childbearing, and likely into the future, by optimizing labor and birth, newborn transitions, breastfeeding, maternal adaptations, and maternal-infant attachment.

There are likely additional benefits from avoiding potential harms of unnecessary interventions, including possible adverse epigenetic programming effects. From the perspective of hormonal physiology, these are not all-or-nothing benefits, but rather accrue along a continuum. Every mother and baby is likely to benefit from  additional support for physiologic childbearing, as far as safely possible, including when interventions are used.”

“Given the uncertainty and potential for significant harms to women and babies in relation to maternity care interventions, application of the Precautionary Principle would be wise in maternity care. Such a standard would involve:

• rigorously verifying the benefits of proposed interventions in individual circumstances before undertaking them
• limiting routine practices to those of proven benefit to healthy mothers and babies
• avoiding the use of interventions for the convenience of women or maternity care providers and systems
• initially using less invasive measures to address challenges, and stepping up to more consequential interventions only as needed” (Sarah Buckley)

Buckley, Sarah J (2015). Hormonal Physiology of Childbearing: Evidence and Implications for Women, Babies, and Maternity Care. Washington DC: Childbirth Connection Programs, National Partnership for Women & Families.

You can download all sorts of goodies from their website, including the full report, an executive summary and a series of factsheets.

Maternal plasma oxytocin

Another of the most important papers about oxytocin and birth in recent years is titled, “Maternal plasma levels of oxytocin during physiological childbirth – a systematic review with implications for uterine contractions and central actions of oxytocin”.

The review was undertaken by a team led by Kerstin Uvnäs-Moberg. Their aim was to collect information about maternal plasma levels of oxytocin during physiological childbirth, and in response to infusions of synthetic oxytocin. In order to do this, the authors gathered data from studies that had looked at this.

The results were clear. Let’s look first at physiological oxytocin levels.

“Basal levels of oxytocin increased 3–4-fold during pregnancy. Pulses of oxytocin occurred with increasing frequency, duration, and amplitude, from late pregnancy through labour, reaching a maximum of 3 pulses/10 min towards the end of labour. There was a maximal 3- to 4-fold rise in oxytocin at birth. Oxytocin pulses also occurred in the third stage of labour associated with placental expulsion. Oxytocin peaks during labour did not correlate in time with individual uterine contractions, suggesting additional mechanisms in the control of contractions. Oxytocin levels were also raised in the cerebrospinal fluid during labour, indicating that oxytocin is released into the brain, as well as into the circulation. Oxytocin released into the brain induces beneficial adaptive effects during birth and postpartum.” (Uvnäs-Moberg et al 2019).

What’s new?

This isn’t necessarily new knowledge, especially to those interested in physiological childbirth. (And I’ve written lots about the pros and cons of induced labour here. And here. But, in a world where evidence is deemed important, it is vital that such knowledge is collected and synthesised through systematic reviews.

What IS new, and a bit surprising, is that the researchers found, “no temporal connection between uterine contractions and oxytocin peaks, even when sampling was very frequent.” (Uvnäs-Moberg et al 2019).

The researchers speculated that this was because of the involvement of the parasympathetic nervous system, which is activated when oxytocin reaches the woman’s brain during physiological labour.

As many will know, oxytocin enhances wellbeing, reduces stress and anxiety and has many beneficial effects relating to pain relief, mother-baby interaction and other aspects of birth.

Does nature know best?

These effects are only experienced when the oxytocin is produced by the mother herself though.

Although the researchers found that, “Infusion of synthetic oxytocin at a rate of 4–9 mU/minute gives rise to oxytocin levels equivalent to levels during physiological labour,” (Uvnäs-Moberg et al 2019), there is a catch.

Synthetic oxytocin, which is given to induce or speed up labour, does not reach the brain.

Thus it does not have the same beneficial effects on the body as a woman’s own oxytocin.

The researchers also note that synthetic oxytocin is often increased to much higher levels than 9mU/minute.

They include a useful discussion on why the use of synthetic oxytocin can be problematic and suggest ways in which this could be addressed.

One of these is to look at whether synthetic oxytocin could be given in a ‘pulsatile’ fashion.

This would still, however, not address the fact that synthetic oxytocin does not reach the brain and help confer the many short and long-term advantages that are gained when the body makes its own oxytocin.

There is lots more in this paper about the relationship of oxytocin to the various stages of labour, and to uterine contractions. It is freely available online and I highly recommend reading it.

Questioning the rationale for exogenous oxytocin

In summary, many women are given exogenous oxytocin during labour and birth. Exogenous simply means that it comes from outside the body, rather than being made within it. It’s the same molecule but the origin is important. That’s because – as above – exogenous oxytocin doesn’t have all the positive effects of oxytocin made by the woman’s own body, and it has downsides too.

As with any intervention, the key is to weigh up the pros and cons for the individual situation.

This can mean not just looking at the pros and cons of exogenous oxytocin itself, but at the bigger picture about why it is being offered, so you can decide whether or not you feel it is justified in your situation.

Two of the key reasons that women are offered exogenous oxytocin in labour – induction of labour and the birth of the placenta – are such big topics that I already have resource pages on them, so these are a great place to find out more.

Post-term pregnancy and induction of labour resources

Placental birth resources

Uvnäs-Moberg K, Ekström-Bergström A, Berg M et al (2019). Maternal plasma levels of oxytocin during physiological childbirth – a systematic review with implications for uterine contractions and central actions of oxytocin. BMC Pregnancy and Childbirth 19: 285.

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