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A large review of studies has found that birth by cesarean section is associated with being overweight and obese in adult life.

Researchers pooled data from 15 studies with a combined population of 142,702 for their analysis. The studies classified overweight as a body mass index of 25 or higher and obesity as 30 or higher, and covered various types of vaginal and cesarean deliveries.

Compared with babies delivered vaginally, those delivered by C-section were 26 percent more likely to be overweight and 22 percent more likely to be obese. The type of vaginal or cesarean delivery — natural, forceps or vacuum extraction vaginal births, or pre-labor or in-labor cesarean deliveries — made no difference.

The analysis, published in the February issue of PLOS One, included a large sample from 10 countries, which gives it considerable strength. At the same time, all studies were observational, and the authors write that further study would be required to establish a causal connection between birth method and adult B.M.I.

“Of course if a C-section is needed for clinical reasons, you’ve got no choice,” said one of the authors, Matthew J. Hyde, a research associate at Imperial College London. “But a woman cannot make a reasoned choice unless she’s fully informed not only about the short-term outcomes, but also the long-term outcomes. We want to give you the data you need to make an informed decision.”