ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: JAMA. 2019 Oct 15;322(15):1515–1517. doi: 10.1001/jama.2019.12925.

The authors merged data from separate national Swedish registers for births and obesity surgery and identified 2921 women who had a Roux-en-Y gastric bypass surgery between 2007 to 2014 (‘cases’) and subsequent pregnancies. Controls were identified as women without bariatric surgery who were matched to cases by many factors, including pre-surgery BMI (mean 43.5), diabetes status, age, smoking and alcohol use. Median interval from surgery to conception was 1.6 years and during that time, cases lost on average 40 kg, and diabetes drug use decreased from 9.7% pre-surgery to 1.5% pre-conception.

The risk of major birth defects was substantially lower (risk ratio, 0.67) in infants of cases (3.4%, 98/2921) than in controls (4.9%, 1510/30 573), including risks of major heart defects and neural tube defects.

These findings show that obesity is teratogenic (possibly mediated by hyperglycaemia). Previous associations between maternal obesity and higher risks for birth defects are well established, but the current findings provide a higher level of causal inference and, importantly, show that reducing BMI pre-pregnancy decreases the excess risk. Furthermore, it allays concerns that any benefits of reducing BMI could be offset by harms of micronutrient deficiency following bariatric surgery, however data were not available on use of micronutrient supplements – it might be that Swedish women are more compliant with this than others.