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Bariatric patients have lower pregnancy weight gain vs non-surgical controls

Women with a history of bariatric surgery had lower pregnancy weight gain than matched controls with similar early-pregnancy characteristics, according to a study by researchers from Sweden. They also found that pregnancy weight gain was lower in those with a shorter surgery-to-conception interval or lower surgery-to-conception weight loss, but did not differ by surgical procedure.

The investigators explained that the association of bariatric surgery with postoperative pregnancy weight gain is not well established and the impact of time and/or weight loss between the bariatric surgery and conception on postoperative pregnancy weight gain is unclear.


Therefore, this nationwide study compared pregnancy weight gain among women with a history of bariatric surgery vs those without. It sought to establish whether pregnancy weight gain after bariatric surgery differs by surgical procedure, surgery-to-conception interval and/or surgery-to-conception weight loss. Using data from the the Scandinavian Obesity Surgery Registry (SOReg), National Patient Register, Prescribed Drug Register, Total Population Register, and Longitudinal Integrated Database for Health Insurance and Labor Market Studies, they identified 547,892 pregnancies between 2014 and 2021 that fulfilled their inclusion criteria, of which 6,394 had a history of bariatric surgery (905 sleeve gastrectomy and 5,489 gastric bypass).


Outcomes

After conducting 1:1 propensity score matching, a total of 12 776 pregnancies were included: 6,388 bariatric surgery pregnancies matched with 6,388 controls. They also conducted a 1:1 propensity score matching, returning 890 gastric bypass matched to 890 sleeve gastrectomy pregnancies.

The mean (SD) age was 31.6 (4.9) years in the bariatric surgery group and 31.4 (5.2) years in matched controls. The mean (SD) early-pregnancy BMI was 29.4 (5.2) in both groups. The BMI category with the most women at the start of pregnancy was overweight (2,606 [40.8%] each in the bariatric surgery and match control groups). All baseline characteristics were well-balanced for the 2 matching procedures, except for education level within the surgery matching (SMD<0.1).


Across all early-pregnancy BMI categories, pregnancy weight gain was lower in women with a history of bariatric surgery, compared with controls matched for early-pregnancy BMI and other factors. The magnitude of difference was largest for women with normal weight or overweight early-pregnancy BMI status, which then decreased stepwise within the obesity subclasses.

The researchers also reported:

  • Among women with a normal weight status, those with a history of bariatric surgery had a pregnancy weight gain z score (equivalent to weight in kilograms at week 40) of −0.23 (13.2 kg), and those without had a z score of 0.10 (14.7 kg), for an adjusted mean difference of −0.33 (95% CI, −0.43 to −0.23).

  • The respective gains were −0.32 (11.9 kg) and 0.01 (13.8 kg), with an adjusted mean difference of −0.33 (95% CI, −0.40 to −0.27) for women with overweight status. The corresponding gains were −0.19 (10.2 kg) and 0.02 (11.6 kg), with an adjusted mean difference of −0.21 (95% CI, −0.29 to −0.13) for women with obese class I status; −0.22 (8.0 kg) and −0.06 (9.1 kg), with an adjusted mean difference of −0.16 (95% CI, −0.29 to −0.03) for those with obese class II status; and −0.16 (6.8 kg) and −0.08 (7.3 kg), with an adjusted mean difference of −0.08 (95% CI, −0.28 to 0.13) for those with obese class III status.

  • Pregnancy weight gain was similar for women with a history of sleeve gastrectomy and gastric bypass (after matching for early-pregnancy BMI and other factors) and across all early-pregnancy BMI categories. There appeared to be a higher weight gain among women after sleeve gastrectomy with a normal weight status (particularly those who were parous) and obese class II and III weight status; however, the 95% CIs for these estimates were either close to 0 or wide, owing to the small sample.

  • Women who conceived within one year after bariatric surgery had the lowest pregnancy weight gain. Thereafter, pregnancy weight gain continuously increased until two years after surgery, decreasing slightly and remaining fairly stable from four to ten years after surgery. Women who conceived within one year after bariatric surgery vs two to less than four years after bariatric surgery gained less weight during pregnancy, regardless of early-pregnancy BMI. This association did not differ by surgery type or parity.

“Women with a history of bariatric surgery gained less weight during pregnancy than those with similar BMI entering pregnancy, which may be attributable to physiological effects of altered anatomy and gut hormones, thereby reducing food intake and appetite,” the authors stated. “…Compared with the controls, a higher proportion of women in the surgery group with a normal, overweight, or obese class I status at the start of pregnancy gained below the pregnancy weight gain guidelines recommended by the US Institute of Medicine. The highest proportion of weight gain below the recommendations was found among women with a normal weight status. Hence, clinical attention to women with history of bariatric surgery and a normal weight status in early pregnancy might be warranted.”


The findings were featured in the paper, ‘Pregnancy Weight Gain After Gastric Bypass or Sleeve Gastrectomy’, published in JAMA Network Open. To access this paper, please click here

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