According to the Centers for Disease Control and Prevention (CDC), the total US Caesarean (C-section) delivery rate in 2011 was at 32.8%, which means a total of nearly 1.3 million babies were delivered this way.
During this procedure, doctors take the baby out of the mother through her abdomen. Most C-sections are performed when unexpected problems occur, such as the position of the baby or signs of distress, but some women choose to deliver this way even in the absence of problems.
Though the surgery is relatively safe, it does carry risks for both the mother and baby. For example, previous studies have suggested babies born by Caesarean are more likely to develop asthma or type 1 diabetes during childhood.
Prof. Neena Modi, senior author from the Department of Medicine at Imperial College London, says:
"There are good reasons why C-section may be the best option for many mothers and their babies, and C-sections can on occasion be life-saving. However, we need to understand the long-term outcomes in order to provide the best advice to women who are considering Caesarean delivery."
The researchers from this latest study note that over the past 20 years, worldwide obesity prevalence in both children and adults has risen. The highest incidences have been reported in the US and Scotland, at 33.8% and 30%, respectively.
To examine potential links between Caesarean births and obesity later in life, the team conducted a review and meta-analysis on 15 studies with over 38,000 participants.
After reviewing the data from 10 countries, they observed that adults born by C-section had a body mass index (BMI) that was half a unit more than those born vaginally, and the odds of being overweight or obese are 26% higher for Caesarean-born individuals.
They say their study is the largest to show a link between C-section delivery and BMI in adulthood.
Though they are not certain that C-section delivery is a cause of higher BMI - since the association could be explained by other factors not recorded - Dr. Matthew Hyde, one of the researchers, says:
"There are plausible mechanisms by which Caesarean delivery might influence later body weight. The types of healthy bacteria in the gut differ in babies born by Caesarean and vaginal delivery, which can have broad effects on health. Also, the compression of the baby during vaginal birth appears to influence which genes are switched on, and this could have a long-term effect on metabolism."
Although strengths of the study include the large population size, the team says a key consideration is "whether the associations we have identified between mode of delivery and offspring outcome are causal or reflect confounding."
Prof. Modi told Medical News Today they now need to determine whether other factors are responsible for the association.
"At the present we are working with pregnant women, their partners and clinical staff to obtain their views on whether a randomized controlled trial of C-section where no medical indication exists would be acceptable to them," she said.
She told us they are also looking into biological mechanisms that could explain the association between obesity and C-section deliveries.
In 2013, Medical News Today reported on a study published in the BMJ journal Gut that suggested C-section infants have fewer "good" gut bacteria.
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