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.

Male vs Female Brains

Women are from Venus and men are from Mars, or so we have long been told. There are obvious physical differences between the sexes, but do these disparities extend to our brains? And if there are sex differences to be found in the brain, are they there from before birth, or are they a product of our upbringing? As well as being interesting areas for scientific study, these questions open up some ethical conundrums - if we did find robust, biological sex differences in the brains of men and women, what would this mean for how we should treat the sexes, and how we should raise our children?

We all have one of these - but are men's and women's brains different?
Image credit: Anatomography, via Wikimedia Commons [CC BY-SA 2.1 jp]

The first, and probably easiest, question to answer is whether there are physical differences in men's and women's brains. We know that males tend to have larger brains than females, and this has been confirmed by a recent meta-analysis^[1]. But do these physical disparities correspond to a difference in ability, or function? Some have argued that larger brain volume suggests greater intelligence, but it is now widely accepted that total brain volume is not a very good indicator of intelligence - Einstein’s brain was actually found to be slightly smaller than average^[2]. A criticism of many studies on brain volume is that they fail to take into account that women, on average, have smaller bodies than men - so it seems reasonable to expect their brains to also be smaller. However brain to body size ratio can’t account for the dissimilarities completely - the correlation between the two is not strong in humans, and boys’ brains remain bigger even at age 11-13, where their bodies are, on average, smaller^[3].

As well as looking at the brain as a whole, researchers look at specific structures inside the brain to see if there is divergence there. The same meta-analysis found size differences in a huge number of structures in the brain, including the amygdala, which is involved in emotional processing and the hippocampus, which is important for memory. Again, these differences weren’t adjusted for the overall distinctions in size between men & women, but as the variations in size and connectivity differed by region it seems it is not just as simple as every area being bigger in men. Discrepancies have also been found in the percentage of grey matter and white matter in the brains of men & women^[4].

Autism: There's Still So Much We Don't Know

Even though autism undoubtedly has biological underpinnings and the brains of those with autism may share some form of common structures (neuroanatomy) or function (neurophysiology), we still don't have a good working definition for it - or at least, nothing that everyone can agree upon. In the field of cancer research, even though scientists disagree about the primary causes of a tumour developing, they can all generally agree that uncontrolled cellular growth is a good working definition. If you see a tumour, you know it's following some sort of poorly-regulated growth process, even when it's benign (non-cancerous). Which makes finding causes of tumour promotion considerably easier. If you know the end result in terms of cell biology, that limits the number of variables you're searching for as instigators of that process.

How people see autism. Image credit: Hepingting

But not so for autism. Even though the well-known psychiatrist, Leo Kanner, described the condition well over 70 years ago, the only thing people can seem to agree upon is a behavioural definition. (And even still, we argue over that!) We have done so much research and have published so many papers reporting correlations with things that may influence the occurrence of autism, ranging from the presence of one or more other disorders or diseases, down to associated genes. But unlike cancer, we have no general definition for what defines autism at the level of the cell nor at the level of the brain. We're still wandering around our research somewhat blindly.

Ultimately, that means we study just about everything that appears to have an association with the condition without much understanding of whether the relationship is causal or simply correlational in nature. An excellent example of this comes from studying autism genetics. Over 3,000 genes have found to have minor-to-strong association with the condition, both those which currently have no known cause (idiopathic) and conditions which are characterized by the association of several clinically recognizable features which tend to go together (syndromic), such as Fragile X Syndrome. While all roads may have once led to Rome, not all genes lead to autism. Those thousands of genes represent at least 12% of the genes within the human genome, a staggering proportion. It's highly unlikely that all or most converge onto a single behavioural trait.