Houston, Texas, USA : Together with colleagues from Sweden and Luxembourg, scientists from the Luxembourg Centre for Systems Biomedicine (LCSB) of the University of Luxembourg have observed that, during a natural vaginal birth, specific bacteria from the mother’s gut are passed on to the baby and stimulate the baby’s immune responses. This transmission is impacted in children born by caesarean section. “This may explain why, epidemiologically speaking, caesarean-born children suffer more frequently from chronic, immune system-linked diseases compared to babies born vaginally,” says the head of the study Associate Prof. Paul Wilmes. His team has now published its results in the open access journal Nature Communications.
Humans are born germ-free. Yet, birth is normally the time when vitally important bacteria start to colonise the body including the gut, skin and lungs. Researchers have long suspected that this early colonisation sets the course for one’s later health. It could be, however, that a caesarean section prevents certain bacteria, ordinarily interacting with the baby’s immune system, from being passed on from the mother to the new-born. Paul Wilmes, head of the Eco-Systems Biology research group at the LCSB, and his colleagues have now found the first evidence of this in a study of new-borns—half of whom were delivered by caesarean section. Wilmes reports: “We find specific bacterial substances that stimulate the immune system in vaginally born babies. In contrast, the immune stimulation in caesarean children is much lower either because the bacterial triggers are present at much lower levels or other bacterial substances hamper these initial immune reactions to happen.”
This bacterial coloniser-immune system link—together with other factors—could explain why caesarean section babies are statistically more prone to develop allergies, chronic inflammatory diseases and metabolic diseases. “It could be that the immune system of these children is set on a different path early on,” suggests Paul Wilmes. “We now want to further investigate this link mechanistically and find ways by which we might replace the lacking maternal bacterial strains in caesarean-born babies, e.g. by administering probiotics.”
“Of course, it is already clear that we should not intervene too strongly in the birth process. Babies should only be delivered by caesarean section when it is medically necessary”, Paul Wilmes stresses. “We need to be aware that, in doing so, we are apparently intervening massively in the natural interactions between humans and bacteria.”
Citation: Linda Wampach et al, Birth mode is associated with earliest strain-conferred gut microbiome functions and immunostimulatory potential, Nature Communications. DOI: 10.1038/s41467-018-07631-x
A second study found a narrower range of helpful bacteria in guts of C-section infants
Narrower range of helpful bacteria in guts of C-section infants
The range of helpful bacteria in the guts of infants delivered by caesarean section, during their first two years of life, is narrower than that of infants delivered vaginally, indicates a small study published online in the journal Gut.
This has implications for the development of the immune system, say the researchers, particularly as the C-section infants had lower levels of the major group of gut bacteria associated with good gut health, Bacteroidetes phylum, as well as chemicals that help curb allergic responses.
The researchers assessed the patterns of bacterial colonisation of the guts of 24 infants, nine of whom had been born by caesarean section one week, and then again at one, three, six, 12 and 24 months after birth.
They also took blood samples at six, 12 and 24 months to test for levels of immune system chemicals known as Th1 and 2 associated chemokines. Excess Th2 chemokines have been implicated in the development of allergies, which Th1 responses can counteract, say the authors.
The results showed that babies delivered by caesarean section, and who therefore did not pass down the mother’s birth canal, either lacked or acquired late one of the major groups of gut bacteria, the Bacteroidetes, compared with the babies born vaginally.
In some C-section infants acquisition of Bacteroidetes did not occur until a year after birth. The total range of bacteria among those born by C-section was also lower than that of their vaginally delivered peers.
The differences in bacterial colonisation between the two groups of infants were not down to their mums having been given antibiotics during C-section or after the procedure to prevent infection: the levels and range of bacteria sampled from both sets of mums were similar, the analysis showed.
Bacteria are important for priming the immune system to respond appropriately to triggers, and not overreact as is the case in allergies, diabetes, and inflammatory bowel disease, say the authors.
This includes the development of immune system T cells and the correct balance between their chemical messengers, Th1 and Th2.
The C-section infants had lower circulating levels of Th1 chemical messengers in their blood, indicating an imbalance between Th1 and Th2. “Failure of Th2 silencing during maturation of the immune system may underlie development of Th2-mediated allergic disease,” write the authors.
They point out that previous research has indicated that Bacteroides fragilis, one of the many Bacteroidetes, strongly influences the immune system, which ultimately enhances T cell activity and the Th1-Th2 balance.
“Thus, the lower abundance of Bacteroides among the C-section infants may be a contributing factor to the observed differences in the Th1-associated chemokines,” they write.
Citation for second study: Decreased gut microbiota diversity delayed Bacteroidetes colonisation and reduced Th1 responses in infants delivered by Caesarean section, Online First, DOI: 10.1136/gutjnl-2012-303249
A third study found that caesarean section delivery may double the risk of childhood obesity.
Caesarean section delivery may double risk of childhood obesity
Caesarean section delivery may double the risk of subsequent childhood obesity, finds research published online in the Archives of Disease in Childhood.
Caesarean section delivery has already been linked to an increased risk of subsequent childhood asthma and allergic rhinitis, and around one in three babies born in the US is delivered this way.
The authors base their findings on 1255 mother and child pairs, who attended eight outpatient maternity services in eastern Massachusetts, USA between 1999 and 2002.
The mums joined the study before 22 weeks of pregnancy, and their babies were measured and weighed at birth, at six months, and then at the age of three, when the child’s skinfold thickness, a measure of body fat, was also assessed.
Out of the 1255 deliveries, around one in four (22.6%; 284) were by caesarean section, and the remainder (77.4%; 971) were vaginal deliveries.
Mums who delivered by c-section tended to weigh more than those delivering vaginally, and the birthweight for gestational age of their babies also tended to be higher. These mums also breastfed their babies for a shorter period.
But irrespective of birth weight, and after taking account of maternal weight (BMI) and several other influential factors, a caesarean section delivery was associated with a doubling in the odds of obesity by the time the child was 3 years old.
Just under 16% of children delivered via c-section were obese by the age of 3 compared with 7.5% of those born vaginally.
Children delivered by c-section also had higher BMI and skinfold thickness measurements by the age of 3.
The researchers speculate that one possible explanation for their findings is the difference in the composition of gut bacteria acquired at birth between the two delivery methods.
They highlight previous research showing that children born by c-section have higher numbers of Firmicutes bacteria and lower numbers of Bacteroides bacteria in their guts. These two groups make up the bulk of gut flora.
Other research has also suggested that obese people have higher levels of Firmicutes bacteria.
It may be that gut bacteria influence the development of obesity by increasing energy extracted from the diet, and by stimulating cells to boost insulin resistance, inflammation, and fat deposits, say the authors.
“An association between caesarean birth and increased risk of childhood obesity would provide an important rationale to avoid non-medically indicated caesarean section,” write the authors.
Mums who choose this delivery option should be made aware of the potential health risks to her baby, including the possibility of obesity, they say.