A history of bariatric surgery is associated with an increased risk of preterm birth and spontaneous preterm birth, according to a report published in the New England Journal of Medicine.

Olof Stephansson, MD, PhD, from the Karolinska Institutet, Stockholm, Sweden, and colleagues previously reported pregnancy outcomes in 590 women who had a history of bariatric surgery and who had given birth between 2006 and 2011 and found no significant association with preterm birth.

However, in an expanded cohort of women who gave birth between 2006 and 2013, the researchers found a significantly higher risk of spontaneous preterm birth (P=.01) among women who had bariatric surgery compared with controls. They did not observe a higher risk of medically indicated preterm birth in women with a history of bariatric surgery compared with controls (P=.56).

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The expanded cohort included 1,941 births from women who had bariatric surgery and 6,574 control births that were matched for maternal pre-surgery BMI, age, smoking status, and delivery year. Of the 1,941 women who underwent bariatric surgery, 163 had a preterm delivery compared with 447 of the 6,574 women in the control group (8.4% vs 6.8%; odds ratio [OR], 1.24).

In addition, the risk of a moderately preterm birth, defined between 32 completed weeks and 36 weeks and 6 days of gestation, was higher among the women who had undergone bariatric surgery compared with the control group (7.3% vs 5.7%; OR, 1.30). There was no significant association observed between a history of bariatric and very preterm birth, which was defined as a birth with <32 weeks of gestation.

The researchers also found a significant inverse association between obesity after bariatric surgery and the risk of preterm birth (P=.03).

“In contrast to the findings reported in our earlier article, we now report a significant association between a history of bariatric surgery and an increased risk of preterm birth and spontaneous preterm birth in particular,” the study authors wrote. “Despite careful matching, differences between the surgery group and the control group may have influenced the results.”


  1. Stephansson O, Naslund I, Neovius M. Bariatric surgery and preterm birth. N Engl J Med. 2016;375:805-806. doi: 10.1056/NEJMc1516566.