A new study published in the open-access journal JAMA Network Open in April 2020 suggests that women born by way of a Cesarean section are at higher risk of developing obesity as well as type 2 diabetes mellitus in adult life.
Over 1.2 million Cesareans take place in the US every year, which means about a third of all births. This is an astounding rise from 2.6% in the 1930s, through 5% during the 1950 - 1970 period, to 24% in 1986. At present, it has steadied at 30%, slightly lower from 33% in 2009. Of these procedures, about half are primary Cesareans performed in women who have not had a previous Cesarean.
The study found an association between being born by cesarean delivery and increased risks of obesity and type 2 diabetes in adulthood. Image Credit: Troyan / Shutterstock
Are Cesareans safer than standard deliveries?
It is well known among obstetricians that a Caesarean is not a piece of cake. The risks of surgical complications are three times greater for a Cesarean than for vaginal delivery in women of the same age, parity, and other comparable factors. These risks include cardiac arrest, having to remove the uterus (to stop bleeding, for instance), infection following childbirth, and venous clots that can travel elsewhere to cause strokes. The babies born this way are more likely to have breathing-related problems. The most important thing is that this increased rate of complications is often preventable.
However, this study examines certain long-term complications caused by Cesarean birth. Several studies have shown a higher risk of obesity in children born this way. Others have shown the risk of abnormalities in several metabolic parameters to be higher. The current study was motivated by the desire to assess how Cesarean birth relates to obesity and type 2 diabetes mellitus.
How was the study done?
The researchers drew their data from the Nurses’ Health Study II, which is a prospective cohort study continuing from 1989 onwards. Updates are collected every two years. In 2001, over 33,000 mothers of women already in the study provided data on their pregnancy with their daughters, to form the Nurses’ Mothers Cohort Study in 2001. The daughters here were born in the period 1946 and 1964.
The mode of delivery of the participating daughter, along with the height and weight at baseline as well as every two years afterward, was available from this data—cases of type 2 diabetes as diagnosed by a physician and confirmed by American Diabetes Association criteria.
What were the findings?
The women participating in the Nurses’ Health Study II were, on average, 34 years old, and 3.3% (about 1,090) were born by Cesarean. The mothers of this subgroup of participants were heavier, before pregnancy, older at delivery, more likely to have high blood pressure induced by pregnancy, at a higher risk of preterm birth, and to bear low birth weight.
Over the available 1.9 million person-years of follow-up, there were over 12,000 cases of obesity and over 2,000 cases of type 2 diabetes. The risk of obesity was 37% among women born vaginally and 40% among those born by Cesarean birth. The number of cases of type 2 diabetes was 10 per 10,000 person-years among those born vaginally, but 14 among those born by Cesarean.
The risk of developing obesity was thus 11% more for those born by Cesarean compared to those born vaginally, after adjusting for multiple factors. For type 2 diabetes, it was 46% higher. When all the eight risk factors such as pregnancy-induced hypertension, smoking, gestational diabetes, maternal obesity, and older maternal age were excluded, there was no significant association between Cesarean birth and these outcomes.
What does the study show about the long-term risks of Cesarean birth?
The study shows a higher risk of both type 2 diabetes and obesity in women born by Cesarean by 46% and 11%, respectively. Why this is so is not altogether clear. However, changes in the gut microbiome of the offspring are being suspected to be partly, at least, responsible. These bacteria regulate the energy balance and may lead to chronic inflammation via exposure to bacterial lipopolysaccharide. Abnormal gut microbiomes can thus result in obesity and in abnormal regulation of blood sugar levels.
The gut microbiome does depend on the mode of delivery, with vaginally delivered babies being quickly colonized by bacteria from the birth canal and feces of the mother, but Cesarean babies by bacteria from the environment. The latter is much less diverse, and the Bifidobacteria/Bacteroides species are fewer in number. These are protective against obesity. The degree to which these changes persist in adulthood is unknown, but they have been shown to persist up to 7 years of age.
Some suggest a change in DNA methylation with Cesarean delivery, but the evidence is less than compelling.
Overall, the findings in favor of increased obesity risk among children born of Cesarean support earlier studies. It is for the first time that a corresponding risk of type 2 diabetes has also been demonstrated in this group, though cardiovascular and metabolic risk factors were shown to be more in young adults born by Cesarean. This study also boasts the most extended period of follow-up, spanning 20-40 years. This brought out the differences in diabetes risk between these groups.
The scientists say, “These findings should be interpreted with caution, given that it is the first time that an association with type 2 diabetes is reported.” More research is needed to confirm these findings and explain the link since this is being reported for the first time.
Chavarro, J. E., Martin-Calvo, N., Yuan, C., et al. (2020). Association of Birth by Cesarean Delivery With Obesity and Type 2 Diabetes Among Adult Women. JAMA Network Open 2020;3(4):e202605. doi:10.1001/jamanetworkopen.2020.2605.