A new study has found that babies born by Caesarean section are twice as likely to become obese by the age of three as newborns delivered vaginally, and authors of the report say women who plan to deliver their babies via C-section because it is more convenient might want to reconsider their options.

The study, conducted by researchers at Children’s Hospital in Boston, monitored 1,250 women from before their 22nd week of pregnancy until they delivered their babies at hospitals in Massachusetts between 1999 and 2002.

Twenty-five percent of the babies were delivered by Caesarean section and the rest were born vaginally.

Height and weight of each baby was taken at three months of age and again at three years of age. Researchers found that by the third year, 16 percent of the C-section toddlers were obese, compared to 7.5 percent of those born vaginally. Differences in the children’s birth weights did not appear to be a factor.

Researchers also found that three-year-olds born by C-section also had a higher skinfold thickness, a measurement of body fat. Although motherhood obesity is a known risk factor for overweight children, researchers said this finding was consistent regardless of the mother’s weight.

According to Dr. Amos Grunebaum, director of obstetrics and chief of labor and delivery at the New York Weill Cornell Medical Center in New York City, it is important to tell mothers who do not need a C-section for medical reasons of the obesity findings and other risks associated with surgical delivery.
“We already know that if you do Caesarean-section, especially when there’s no medical indication, there’s an increased risk of babies being admitted to the intensive care unit for breathing issues,” he said, adding that there are a number of legitimate reasons for a C-section, including babies who are positioned buttocks or feet first in the birth canal, and babies in distress or whose births are not progressing normally.

The Massachusetts researchers have speculated that obesity may be influenced by bacteria in a newborn’s gut, which could be different in C-section babies than in vaginally-delivered babies. The microbes, they said, could affect how calories and nutrients are absorbed from food, promoting insulin resistance, inflammation and fat.

Another possibility, researchers said, is that hormones released during labor may influence the development of obesity, but that both possibilities need further study.

Grunebaum said he is likely to inform patients seeking an elective C-section of the additional risk of obesity.

“Whenever we do any procedure, we balance risks with benefits,” he said. “And if risks outweigh benefits - and in this case there are some risks such as obesity versus very little benefits - then women should be aware of this.”

A study on Caesarean section and the increased risk of childhood obesity is published in the journal Archives of Disease in Childhood.

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Jessica Berman