My favourite birth-related research paper this month (by a very long way) is about oxytocin and birth. It’s 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 and its 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).
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). 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.
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.