Bariatric surgery before pregnancy linked to lower risk of gestational diabetes

1. Bariatric surgery in obese patients before pregnancy was associated with a lower incidence gestational diabetes, large-for-gestational infants, and macrosomia.

2. The incidence of stillbirth and neonatal death was slightly higher in mothers who underwent bariatric surgery; however, this was of only borderline statistical significance.

Evidence Rating Level: 2 (Good)

Study Rundown: Obesity is defined as having a body-mass index (BMI) of greater than 30 kg/m2. While obesity is commonly linked to cardiovascular comorbidities, obesity during pregnancy is a key risk factor for the development of gestational diabetes and subsequent complications such as macrosomia, complications at delivery, and an increased risk of future type 2 diabetes. Prior small studies have shown that bariatric surgery prior to conception may have benefits in terms of reducing pregnancy risks to both mother and fetus.

Using a national Swedish registry, this retrospective cohort study first identified obese women who underwent bariatric surgery and then found similar obese pregnant women who did not undergo bariatric surgery. The groups were well matched for maternal age, BMI, smoking status, educational level and nulliparity.

Compared to matched controls, those with pre-pregnancy bariatric surgery had a statistically significantly lower incidence of the following: gestational diabetes, large-for-gestational infant, and macrosomia. However, bariatric surgery increased the risk of infants being small for gestational age. The incidence of stillbirth or neonatal death was higher in the bariatric surgery group; however, this was only of borderline statistical significance.

This study garners strength from the large size of the cohorts under consideration. The database used for the study involved mostly Caucasians from Sweden; therefore, results cannot be generalized to other ethnicities. While the bariatric-surgery cohort was well matched to the control cohort based on a number of key potential confounding factors, other important yet unaccounted characteristics between the matched groups may have been missed. Future studies will be required to better understand the finding of increased incidence of stillbirths and neonatal death in the bariatric surgery group (which reached marginal significance).

Click to read the study, published today in NEJM

Click to read an accompanying editorial in NEJM

Relevant Reading: Obesity in Pregnancy (Committee Opinion) – The American College of Obstetricians and Gynecologists

In-Depth [retrospective cohort]: This nationwide Swedish cohort study retrospectively examined the incidence of gestational diabetes and other perinatal outcomes from two matched cohorts (from 2006-2011): bariatric surgery for obese women before pregnancy (median 1.8 years prior to pregnancy) and no bariatric surgery for obese women before pregnancy. Up to five control pregnancies (without bariatric surgery) were matched to the bariatric surgery cases. Matched data involved 596 births to 554 mothers after bariatric surgery and 2,356 matched control births to 2,278 mothers without bariatric surgery. The two groups were well matched for maternal age, smoking status and educational level. Mean body-mass index and the baseline incidence of certain comorbidities (respiratory disease, psychiatric disease and substance abuse) were higher in the bariatric surgery groups (p<0.001 for all).

Patients undergoing bariatric surgery before pregnancy were less likely to develop gestational diabetes (OR 0.25, p<0.001) or to have large-for-gestational age infants (OR 0.33, p<0.001). However, the risk of small-for-gestational age infants was higher in the bariatric surgery group (OR 2.20, p<0.001), as was the risk of stillbirth or neonatal death (1.7% in the bariatric surgery group versus 0.7% in the non-bariatric surgery group, OR 2.39, p=0.06). There was no difference between the two groups in terms of major congenital malformations (OR 0.72, p=0.27) or low birth weight infants (OR 1.34, p=0.17).

Image: CC/Nancy Price

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