What time are babies most likely to be born?
As a home birth midwife, I’m well aware that a good many babies like to be born in the deep of the night. They will often wait until everyone has gone to bed, and then decide to properly make their move. I couldn’t count the times that my pager or phone has woken me just half an hour after I laid my head on a pillow. It’s just how things are. (I had one mentor, when I was a student midwife, who always did her hair beautifully before she went to bed, for this very reason. She had been caught out too many times!)
Often, the baby will be born in the wee hours, enabling me to make that most delightful journey home. Just as everyone else is getting up and starting their day, I am (other work and babies permitting) heading back to the comfort of my own bed, having left a new family tucked up in theirs.
The rhythm of labour
So I was really interested to come across a newly published study which looked at whether and how neuraxial analgesia has an effect on the circadian rhythm of labour. My interest, if I’m honest, is more in what the physiological rhythm of labour is. That’s partly because, as the authors of the study note, previous studies have shown varying results.
Let me propose, if I may, a reason for this discrepancy, which is also a limitation of the current study and something to bear in mind as you read. Like most of the studies that I have seen on this topic, this research is based on data from hospital births. So it’s not capturing what might happen if women were labouring at home or in an environment that fully supported female physiology. This isn’t the only reason that might explain the variation in results between studies, but it’s an important one. For more on how research into labour is affected by most of the data being gathered from medicalised, hospital births, see Nadine Edwards’ excellent book, Birthing Your Baby.
The study’s aims
The authors of this study “aimed to confirm whether there was delivery rhythm, and to investigate whether the neuraxial labor analgesia [NA] or other intervention factors have effects on it” (Wang et al 2022). They collected retrospective data from 43,577 births that took place between January 1, 2016 and December 31, 2018 from seven hospitals in Boston, USA. Women who had caesarean sections, stillborn or breech babies were excluded, and the authors also excluded any cases where full data weren’t available.
That raises another couple of the limitations that we always need to think about. Retrospective study designs are reliant on the accuracy of medical and maternity records, which aren’t always all that accurate. Such designs can also lead to particular types of bias. It’s also important to remember that the USA has a particularly medicalised approach to birth which isn’t always similar to the approach taken in other countries.
But no research design is perfect, and on the whole this is a very reasonable approach to take to collect data of this kind. We always need to consider the downsides and possible limitations of any form of evidence before we adopt it into our worldview or practise. I’ll mention now that the researchers did include women whose labours were induced or augmented. It’s important to know that the drugs used for this would arguably have been even more likely to impact delivery time than neuraxial analgesia. But the researchers were aware of this, and I’ll come back to it.
So what time ARE babies most likely to be born?
The researchers looked at two groups. “NAD was defined as a delivery with NLA, such as epidural anesthesia, spinal anesthesia, or combined spinal and epidural anesthesia. SVD was defined as a delivery without NLA.” (Wang et al 2022).
When you read the abstract of the study, it seems to suggest that there is a clear peak of births in the SVD group between 02.00 and 04.00. And yes, ten per cent of babies were born in that period, whereas around seven, eight or nine per cent were born in each of several of the other two-hour periods. (See the table here if that doesn’t make sense). The time span has the highest rate of births, for sure. But the peak isn’t a peak in the way that a hill has a peak. It’s more of a gentle hump.
That may be because the high rate of induction and augmentation, on top of the medicalised approach, is having more of an influence on birth time. It could be for other reasons too. Or maybe every baby is different and there isn’t a circadian rhythm to labour, despite our thinking there might be. We just don’t know. The authors do break down the data in several categories. However when I reached that point of the paper, I was approaching the conclusion that either there is little that we can uncover as far as the timing of spontaneous birth is concerned, or the level of intervention experienced by those whose data were collected is masking any difference.
The table showing the time of birth for babies born after their mums had a spinal or epidural is interesting. It shows that those babies whose mums had NA and who were born by spontaneous vaginal birth were more likely to be born between ten in the evening and six in the morning. I have italicised those words for a reason. The data also show that women who had an instrumental birth (remembering that those who had caesareans weren’t included) were more likely to give birth during the day. That’s also consistent with what many of us see in practise, and midwives and obstetricians have long speculated and written about why it is that more intervention seems to happen during the day rather than at night. That’s too big a debate to enter into here though.
Unsurprisingly, more of those who had their labour induced ended up having a spinal or epidural. That might be because of the increased pain that comes about with induced or augmented labour. More on that here.
What can we learn?
I find one thing about this study (and many of those like it) fascinating. The authors note that:
“The biological rhythm referred to the phenomenon that the physiology and behavior change periodically in all living things. It was the inherent feature of life activities, even in the absence of light, but can be interfered by the external environment … Labor also has a circadian rhythm. The circadian rhythm of labor was altered due to the intervention of labor induction, oxytocin and operative delivery.” (Wang et al 2022).
The conclusion of the paper is, for me, the most interesting part. The authors begin to speculate about the ways in which the 24-hour light, noise and interferences found within a labour ward environment, and in the world in general, might also affect the rhythm of labour.
“Varea, C  showed the peak period of childbirth was at 4:00 at the end of the nineteenth century in Madrid, Spain. Charles, E  showed the peak was at 0:00–4:00 am from 1949 to 1951 in Birmingham, England. Because there were no other medical interventions and less influence from the surrounding environment such as artificial lighting at that time, so it was closer to the natural state. The earlier peak and nadir of the birth time may be related to modern rest-activity rhythm and illumination of modern society, which was different from that of a hundred years ago when there was no modern obstetric intervention and artificial lighting .” (Wang et al 2022).
The wider issues
When I picked up this paper, I was interested in the question of what time are babies most likely to be born. I was also curious as to whether the data showed a clear difference between the time of birth with and without a spinal and/or epidural. In fact, the issues it raises are far more complex than this. Having just written a book in which I detailed a whole body of literature showing the value of women going into labour in their own time (rather than having their labour unnecessarily induced), I was fascinated to return to the question of birth timing. And this (freely available) paper is a great start if you’re keen to explore it yourself.
One of the things I took away was a renewed sense of how much our interference affects birth. And by interference, I don’t just mean professionals, interventions and hospitals. We should also consider the impact of electric lighting, our 24-hour society and the well-meaning partner, birth worker or friend who sits beside you in the middle of the night looking things up on their phone. If we want to truly understand birth, we need to step beyond our preconceptions and existing beliefs. We need to challenge our current ideas, be willing to think outside the box, go beyond the obvious and step outside the polarising dichotomies which seem to characterise our age. Things are so rarely clear cut, and one size never fits all.
There’s always a danger, though, when writing about topics like this, of being accused of trying to shame those who seek to do particular things. That might be having particular forms of pain relief, using their phone at night or opting for interventions. That’s not the intention here at all. This is about exploring the issues and options, so that anyone making decisions about any kind of health care, treatment or intervention can think about the bigger picture. This might also include information about the pros and cons of different approaches, so that everyone make the decisions that are right for them. Different people have different values, concerns and priorities and one size never fits all.
Wang L, Ma X, Chen L et al. (2022). Neuraxial analgesia interfered with the circadian rhythm of labor: a propensity score matched cohort study. BMC Pregnancy Childbirth 22, 6 (2022).