Maternal obesity, interpregnancy weight changes and congenital heart defects in the offspring: a nationwide cohort study

Abstract Objective To evaluate the association between maternal BMI and congenital heart defects (CHDs) in the offspring when including live births, stillbirths, aborted and terminated pregnancies and to investigate if maternal interpregnancy weight changes between the first and second pregnancy influences risk of foetal CHDs.Methods A nationwide cohort study of all singleton pregnancies in Denmark from 2008 to 2018. Data were retrieved from the Danish Foetal Medicine Database, which included both pre- and postnatal diagnoses of CHDs. Children or foetuses with chromosomal aberrations were excluded. Relative risks were calculated using log-linear Poisson models for CHDs overall, severe CHDs and for five of the most prevalent subtypes of CHDs.Results Of the 547 178 pregnancies included in the cohort, 5 498 had CHDs (1.0%). Risk of CHDs became gradually higher with higher maternal BMI; for BMI 30-34.9 kg/m², adjusted relative risk (aRR) 1.23 (95% CI 1.12–1.36), for BMI 35-39.9 kg/m², aRR 1.26 (95% CI 1.09–1.46) and for BMI ≥ 40 kg/m², aRR 1.81 (95% CI 1.50–2.15). Data was adjusted for maternal age, smoking status and year of estimated due date. The same pattern was seen for the subgroup of severe CHDs. Among the atrioventricular septal defects (n = 245), a particularly strong association with maternal BMI ≥ 40 kg/m² was seen, aRR 4.19 (95% CI 2.13–7.42). 107 627 women were identified with their first and second pregnancies in the cohort. Interpregnancy BMI change was associated, albeit not statistically significant, with risk of CHDs in the second pregnancy when adjusting for maternal age and BMI, with an aRR 1.27 (95% CI 0.96–1.64) among persons with a BMI increase of ≥ 4 kg/m².Conclusion Risk of foetal CHDs became gradually higher with higher maternal BMI, but only a non-significant association was seen for interpregnancy weight changes and risk of CHDs.