Association of maternal gestational weight gain with intellectual developmental disorder in the offspring: a nationwide follow-up study in Sweden.

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To investigate the association between maternal gestational weight gain (GWG) and offspring's intellectual developmental disorders (IDD); how this association is modified by maternal early-pregnancy BMI. Population-based cohort study. All liveborn singletons with information on maternal GWG in the Swedish Medical Register during 1992-2006 (n = 467 485). We used three GWG classifications, (1) Institute of Medicine (IOM) guidelines ('ideal' GWG: maternal underweight = 12.7-18.1 kg; normal = 11.3-15.9 kg; overweight = 6.8-11.3 kg; obesity = 5.0-9.1 kg), (2) LifeCycle project recommendation ('ideal' GWG: maternal underweight = 14.0-16.0 kg; normal = 10.0-18.0 kg; overweight = 2.0-16.0 kg; obesity class I = 2.0-6.0 kg; obesity class II ≤0.0-4.0 kg; obesity class III ≤0.0-6.0 kg) and (3) GWG centiles. Hazard ratio (HR) and 95% CI for offspring's IDD risk using Cox regression. IDD was extracted from Swedish National Patient Register (code ICD-9:317-319/ICD-10:F70-F79). Forty-one per cent of children were born to mothers with excessive GWG, 32.8% with ideal GWG and 26.2% with inadequate GWG according to IOM guidelines. Inadequate GWG was associated with 21% higher risk of offspring's IDD (95% CI 1.11-1.31) relative to ideal GWG. In contrast, when using the LifeCycle classification, children of mothers with inadequate GWG (HR 1.14, 95% CI 1.05-1.24) or excessive GWG (HR 1.09, 95% CI 1.01-1.17) had higher risks of IDD than those of mothers with ideal GWG. When using GWG centiles, extremely low GWG (<20th centile) and low GWG (20th-40th centile) were associated with elevated offspring's IDD risk. Further stratified analysis by maternal early-pregnancy body mass index (BMI) showed that overweight/obese mothers (BMI ≥25 kg/m2 ) with extremely excessive GWG (>25 kg) was associated with an increased offspring's IDD. Our findings suggest that inadequate maternal GWG may increase offspring's IDD risk, irrespective of maternal early-pregnancy BMI. Extremely excessive GWG (>25 kg) may increase offspring's IDD risk, but only among mothers with an early-pregnancy BMI ≥25 kg/m2 . Inadequate maternal weight gain during pregnancy may increase the risk of offspring's intellectual disability, regardless of maternal BMI.