Preconception Bariatric Surgery May Cut Risks for Mom, Fetus

Diana Swift

February 26, 2015

Obese woman who undergo bariatric surgery before pregnancy have reduced risks for gestational diabetes (GD) and large-for-gestational-age infants, according to the largest study of this patient population to date. However, they also have greater risks for small-for-gestational-age infants.

The authors conclude that post–bariatric surgery mothers need increased surveillance in pregnancy and the neonatal period. The national cohort study was published in the February 26 issue of the New England Journal of Medicine.

Kari Johansson, PhD, from the Clinical Epidemiology Unit, Karolinska Institute, Stockholm, Sweden, and colleagues compared the risks for GD and various adverse perinatal outcomes in women previously treated with bariatric surgery (98% gastric bypass) for weight loss and in matched control patients who had not had bariatric surgery.

Apart from GD and size for gestational age, the study also looked at rates of preterm and stillbirth, neonatal death, and major congenital malformations.

Researchers identified 628,778 singleton pregnancies entered in the Swedish Medical Birth Register between 2006 and 2011. Of these, 670 pregnancies occurred in 616 mothers with a history of bariatric surgery between 2004 and 2011. For each of the case pregnancies, the researchers matched as many as five control pregnancies for a mother's presurgery body mass index (BMI; early-pregnancy BMI in controls) age, parity, smoking history, educational level, and year of delivery. Overall, the investigators included 627,023 control births to 479,624 mothers.

Compared with women in the general population, the surgery cohort tended to be older, obese, and multiparous, as well as more likely to smoke and have lower educational levels (P < .001), but these differences were eliminated in matching surgery cases to controls.

In an accompanying editorial, however, Aaron B. Caughey, MD, PhD, from the Department of Obstetrics and Gynecology, Oregon Health and Science University, Portland, notes that the researchers did not account for some potentially important confounders, such as previous pregnancy complications, or for possible fundamental differences between women who choose bariatric surgery and those who do not.

Compared with control patients, the surgery group had slightly but significantly higher average presurgery BMI (mean between-group difference, 0.5) and a history of more hospitalizations for substance abuse and cardiovascular, respiratory, and psychiatric disease.

In the surgical group, 14% had presurgery diabetes, and the median interval from surgery to delivery was 1.8 years (interquartile range, 1.4 - 2.5 years). The mean presurgery BMI was 43.7 kg/m2, and the mean weight loss between surgery and pregnancy was 37 kg, for a mean decrease in BMI of 13.4 kg/m2.

Gestational weight gain was similar in the two groups, at 8.8 kg in postsurgical pregnancies and 9.0 kg in control pregnancies.

In the postsurgery group, 1.9% of the women developed GD vs 6.8% of the women in the control group (odds ratio [OR], 0.25; 95% confidence interval [CI], 0.13 - 0.47; P < .001). In both groups, GD diagnosis was made at a median of 32 weeks' gestation.

The postsurgery group also had a lower proportion of large-for-gestational-age infants compared with the women in the control group (8.6% vs 22.4%; OR, 0.33, 95% CI, 0.24 - 0.44; P < .001). Macrosomia risk in the surgery group was 1.2% vs 9.5% in the control group (OR, 0.11; 95% CI, 0.05 - 0.24; P < .001).

Postsurgery pregnancies were associated, however, with a 15.6% risk for small-for-gestational-age pregnancies vs 7.6% for control pregnancies (OR, 2.20; 95% CI, 1.64 - 2.95; P < .001). They also showed a nonsignificant trend for increased risk for low birth weight, at 6.8% vs 4.5% (OR, 1.34; 95% CI, 0.88 - 2.04; P = .17).

Although the postsurgical group had, on average, slightly shorter gestation than control pregnancies (273.0 vs 277.5 days), the risk for preterm birth was similar in both groups, at 10.0% compared with 7.5% (OR, 1.28; 95% CI, 0.92 - 1.78, P = .15).

The researchers also saw a trend for increased risk of stillbirth or neonatal death among the postsurgery pregnancies compared with the control pregnancies, but the difference did not reach statistical significance (1.7% vs 0.7%; OR, 2.39; 95% CI, 0.98 - 5.85; P = .06).

Despite the adverse effects of gastric bypass surgery on the metabolism of nutrients such as iron, vitamin B12, and folate, there was no significant between-group difference in the frequency of major congenital malformations, at 2.4% and 3.5%, respectively. "Still, we cannot exclude the possibility that risk of specific malformations differed between the two groups," Dr Johansson and colleagues write.

The authors note several study limitations, including its observational nature, which cannot determine cause and effect, and the potential for selection bias because the bariatric group might have been followed more closely postsurgery for diabetes, whereas unrecognized diabetes might have been overrepresented in the control group. Furthermore, the findings' generalizability might be limited because most study mothers were of white Swedish descent.

Although acknowledging that preconception bariatric surgery has the potential to reduce some pregnancy risks, Dr Caughey notes that the American College of Obstetricians and Gynecologists advises women to delay conception for 12 to 24 months after surgery, the period of most rapid weight loss.

In addition, the type of weight-loss surgery is also important. "In particular, those who have undergone the traditional Roux-en-Y gastric bypass surgery are at increased risk for protein, iron, vitamin B12, vitamin D, and calcium deficiencies; screening for these deficiencies is recommended by the [American College of Obstetricians and Gynecologists]," he writes.

"Decisions regarding bariatric surgery in women of reproductive age should take into account the benefits and risks of this not inconsequential procedure in terms of both pregnancy and long-term risk," Dr Caughey concludes.

This study was supported by grants from the Karolinska Institute, the Swedish Research Council, the Obesity Society, and the Stockholm County Council. One author reported receiving private sector consulting fees outside of this work from Itrim and Strategic Health Resources. The other authors and the editorialist have disclosed no relevant financial relationships.

N Engl J Med. 2015;372:814-824, 877-878. Abstract

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