You aren’t quite as human as you might think. Th e multitudes of microbes that live within and on your body – collectively known as the microbiome – outnumber your human cells by ten to one. As you emerged into the world, microbes from your mother’s gut and skin began to colonise your digestive tract – a phenomenon that scientists suspect helps to prime your early immune system. If you were born by caesarean section (CS), however, you may not have been exposed to the full complement of microbes from your mother and your microbiome may have taken a little longer to develop properly.
CS deliveries are on the rise. In 2015, 29.7 million births (21.1 per cent of all births worldwide) occurred by CS – a huge increase from 16 million (12.1 per cent) in 2000. Epidemiological studies published in The Lancet show that the number of CS babies has jumped by more than five per cent annually. Countries where CS occurs in more than 15 per cent of births are more likely to have higher levels of socioeconomic development, women’s education and urbanisation, and a higher density of physicians. Latin American and Caribbean countries top the charts, with highs of 44.3 per cent of births by CS. However, those where CS occurs in fewer than ten per cent of births are more likely to have higher fertility rates, such as in western Africa.
Researchers have pinpointed a few reasons for the rise: first, the proportion of births occurring within medical centres has risen across much of the world. Second, the skills and equipment necessary to perform CS are more widespread. Shifting cultural attitudes may also contribute. Planning the delivery of a baby through CS can allow families to prepare for the new arrival.
However, access to CS interventions may come at a price. ‘The immune system of babies in utero is not developed. The development begins the moment the baby sees the outside world,’ explains Willem De Vos, professor of human microbiomics at the University of Helsinki. Some of the first microbes that newborns are exposed to are those from the mother’s digestive tract and vagina. Within hours, maternal gut bacteria begin to colonise the babies’ digestive systems.
Scientists believe that this process is a natural ‘primer’ for an infant’s immune system. ‘The gradual development of the microbiome in early life seems to parallel the immune development of infants,’ says De Vos. ‘How exactly this works, we don’t fully know, but the hypothesis is that immune development is induced by these microbes.’ CS babies, on the other hand, may miss out on this process. ‘CS babies don’t have the same temporal development of the microbiome as those born vaginally,’ says De Vos. In early life, many of the bacterial species identified in babies born vaginally are almost absent from the microbiomes of babies delivered by CS.
Some scientists suspect that these stunted microbiomes could be behind an observed increase in immune and developmental disorders worldwide. The incidence of inflammatory bowel disease is on the rise worldwide; in UK children under five, the incidence of type 1 diabetes is currently rising by five per cent each year. ‘We are increasingly seeing associations between CS incidence and some later-life immune disorders, and that’s why I think it’s important to follow this developing field,’ says De Vos. A recent study that assessed more than 2.5 million CS births in Denmark between 1982 and 2010 showed an increased risk of chronic immune disorders, such as inflammatory bowel disease, type 1 diabetes, rheumatoid arthritis and coeliac disease. In the USA, a study published in the American Journal of Epidemiology reported that babies born by CS are more susceptible to food allergies in later life.
Because of these emerging links, microbiome scientists are researching ways to ‘normalise’ the microbiomes of CS babies. Some formulations of probiotics already contain microbes that can help, but they fail to restore all of the important species. De Vos, alongside clinicians working with the Human Microbiome Research Program, has a simpler, if slightly unpalatable solution: ‘The most natural and cost-effective way to inoculate the term-infant gut is to expose the infant to maternal intestinal bacteria: in this case, through exposure to the mother’s feces.’
Armed with this simple hypothesis, his team recruited 17 pregnant mothers into a clinical trial. They collected fecal samples from the mothers three weeks before their due date and scanned them for disease-causing pathogens. They then mixed the highly diluted fecal matter into the mothers’ breast milk, before feeding the mix to their newborn babies – a procedure they dubbed a ‘fecal transplant’. When they compared the microbiomes of those born vaginally to CS babies with and without fecal transplants, they found that CS babies that received fecal transplants had microbiomes resembling those of vaginally born babies. ‘Our study showed that a small fecal transplant from mother to infant allows the bacteria to colonise the infant gut as you would expect from a vaginal delivery,’ says De Vos.
There is still more work to be done: ‘It’s not sufficient to say this should be a routine medical treatment,’ says De Vos. ‘We first have to understand the long-term effects on the immune system.’ Studies are now under way to carry out this long-term monitoring.