Weight-loss surgery tied to lower risk of birth defects

Women with severe obesity who have gastric bypass surgery to lose weight before becoming pregnant may be less likely to have babies with birth defects than similar women who don’t have weight-loss surgery, a new study suggests.

As reported in JAMA, researchers examined data on more than 33,000 women with a history of severe obesity who gave birth, including 2,921 who had gastric bypass surgery and lost weight before conception. Overall, 3.4% of women who had surgery had babies with major birth defects, compared with 4.9% of women who didn’t have weight-loss operations.

Changes in weight and blood sugar may explain these results, said lead study author Martin Neovius, from the Karolinska Institute in Stockholm.

“Both obesity and poorly controlled blood sugar are associated with increased risk of birth defects in a dose-dependent manner,” Neovius said by email. “This means that the more obese you are, the greater the risk of birth defects, and the worse blood glucose control, the greater the risk of birth defects.” In the surgery group, women started out with an average body mass index (BMI) of 43.5 and an average weight of 122 kilograms (269 pounds). After surgery, their average body weight was 82 kilograms (181 pounds) prior to conception.

Before gastric bypass surgery, 9.7% of the women in that group had been taking prescription diabetes drugs to lower their blood sugar. But in the six months prior to conception, only 1.5% of them took diabetes drugs.

“These improvements may be the mechanism behind the observed lower risk of birth defects,” Neovius said.

Major heart defects accounted for 60% of the birth defects among mothers who underwent gastric bypass procedures. No babies in this group had neural tube defects, while there were 20 cases of neural tube defects among women who didn’t have surgery.

For the study, researchers examined data on singleton births in Sweden from 2007 to 2014.

All of the weight-loss surgeries were procedures known as Roux-en-Y gastric bypass, in which surgeons divide the stomach to create a small pouch about the size of an egg. Then, surgeons connect the pouch to the end of the small intestine, so that food travels directly there, bypassing the stomach and the first portion of the small intestine.

One limitation of the study is that it only included data on live births, not miscarriages or pregnancy terminations or stillbirths. It’s possible the results might underestimate birth defects by excluding these pregnancies, at least some of which might have ended because babies had birth defects too severe to survive.

Obesity can contribute to infertility, noted Dr. Brian Smith, co-director of the minimally invasive surgery fellowship at UC Irvine Health and chief of surgery at the VA Long Beach Healthcare System.

“Many women elect to undergo bariatric surgery in order to facilitate pregnancy and/or treat polycystic ovary syndrome, a major contributor to infertility,” Smith, who wasn’t involved in the study, said by email.

“Fewer birth defects appears to be yet another important health benefit of weight loss surgery (specifically gastric bypass), and women considering pregnancy and bariatric surgery should consider postponing pregnancy until after they have achieved meaningful postoperative weight loss and their weight is stable,” Smith said.

Weight loss without surgery may also help, however.

“One can also infer that non-surgical weight loss MAY have similar benefits in reducing birth defects if women are able to achieve similar blood glucose control through diet and exercise alone,” Smith added.