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Friday, 20 March 2020

Caesareans (Things We Don’t Know about Pregnancy Series #15)

Historically, a caesarean section was a life or death operation. When a birth started to go wrong, the question was who to save – the mother, or the baby? Luckily, the maternal mortality rate for pregnancy has dropped to around 0.007% in the UK in 2017 (down from 0.09% in just 1952[1]), and caesarean sections are now considered only slightly more risky than vaginal births (death risk is 3 times higher[2], but this may be because a number of caesareans are only carried out in emergencies). Caesareans may also reduce the risk of complications in some cases. It used to be that having a caesarean once meant further babies always had to be delivered this way – but that’s no longer true: for women who have previously had a caesarean section, choosing an elective one for a subsequent baby over a vaginal birth reduces the risk of complications or consequential health problems (such as womb damage) from 1.8% to 0.8%[3]. However, risk overall is small.

Caesareans now account for 26.2% of births in the UK[4], but there is still a lot we don’t know about them, especially how they might affect babies later in life.

Caesarean by Salim Fadhley via Wikipedia Commons.

Microbiome


Definitely the most talked about mystery surrounding caesarean births is the microbiome, or colony of gut microflora, found in babies born through caesarean section. Compared to babies born vaginally, it’s different: noticeably different[5]. Researchers suspect that the early microbiome could be key to explaining the long-term health of babies, children and adults – but we don’t know. So far, studies done in mice have linked caesarean birth to obesity and compromised immune systems[6], but it’s unclear how long the influence of caesarean on the microbiome persists: i.e. does the microbiome of a caesarean-born baby become indistinguishable from a virginally born baby and, if so, how long does it take? We know that the mother’s diet can affect the microbiome of a baby before it’s even born, and there are a myriad of influences once it is.

Controversially, some practitioners have started swabbing caesarean babies with vaginal fluids (known as vaginal seeding) in case it helps[7].

Developmental Disorders


Regardless of whether elective or emergency, a review of 20 million births across 61 studies has shown that babies born by caesarean are a third more likely to develop autism and a sixth more likely to develop ADHD[8]. Scientists don’t know why.

Possible explanations include

- Confounding factors that contribute to the likelihood of a caesarean, like an older mother, defective placenta, or premature baby.
- Use of antibiotics during the operation.

But it seems unlikely it is linked to mode of delivery. Nevertheless, in some countries such as Nigeria caesarean birth is still considered shameful, and women are pressurised into trying for a natural birth even when it is dangerous to prove themselves “real women”.

Baby cries


Baby by Beth [CC BY 2.0], via Flickr.
Mysteriously, another caesarean link researchers have uncovered lies in the maternal brain response to their baby’s cry. Studies have shown that parents recognise their own baby’s cries above those of others[9] and are more responsive to their needs due to an amplifying effect of the hormone oxytocin[10]. The effect, however, is not as strong if the baby is delivered by caesarean section[11]. Fathers are equally good at recognising their own baby’s cry as mothers[12], but, for some reason, they are less sensitive to oxytocin, and giving them more doesn’t seem to increase their sensitivity to baby cries[13].


There are many unknowns when it comes to pregnancy, and over the next few months, I’ll be exploring more of them with you. Look out for my next blog post, which will be about how much unborn babies sleep.
 

To read our full article on the things we don't know about pregnancy, check out our site. This article will be updated as we add posts across the coming months.


References
why don't all references have links?

[1] Maternal, Newborn. Saving Lives, Improving Mothers’ Care. (2014).
[2] Deneux-Tharaux, Catherine, et al. Postpartum maternal mortality and cesarean delivery. Obstetrics & Gynecology 108.3 (2006): 541-548.
[3] Fitzpatrick, Kathryn E., et al. Planned mode of delivery after previous cesarean section and short-term maternal and perinatal outcomes: A population-based record linkage cohort study in Scotland. PLoS medicine 16.9 (2019).
[4] Shao, Yan, et al. Stunted microbiota and opportunistic pathogen colonization in caesarean-section birth. Nature 574.7776 (2019): 117-121.
[5] Dominguez-Bello, M. G. et al. Proc Natl Acad. Sci. USA 107, 11971–11975 (2010).
[6] Martinez, Keith A., et al. Increased weight gain by C-section: Functional significance of the primordial microbiome. Science Advances 3.10 (2017): eaao1874.
[7] Nature 572, 423-424 doi: 10.1038/d41586-019-02348-3.
[8] Zhang, Tianyang, et al. Association of cesarean delivery with risk of neurodevelopmental and psychiatric disorders in the offspring: a systematic review and meta-analysis. JAMA network open 2.8 (2019): e1910236-e1910236.
[9] Formby, David. Maternal recognition of infant's cry. Developmental medicine & child neurology 9.3 (1967): 293-298.
[10] Marlin, Bianca J., et al. Oxytocin enables maternal behaviour by balancing cortical inhibition. Nature 520.7548 (2015): 499.
[11] Swain, James E., et al. Maternal brain response to own baby‐cry is affected by cesarean section delivery. Journal of child psychology and psychiatry 49.10 (2008): 1042-1052.
[12] Gustafsson, Erik, et al. Fathers are just as good as mothers at recognizing the cries of their baby. Nature Communications 4 (2013): 1698.
[13] De Pisapia, Nicola, et al. Gender differences in directional brain responses to infant hunger cries. Neuroreport 24.3 (2013): 142.

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