The associations between maternal pre-pregnancy body mass index or gestational weight change during pregnancy and body mass index of the child at 3 years of age.

OBJECTIVE: To estimate the associations between maternal pre-pregnancy body mass index (BMI) or gestational weight change (GWC) during pregnancy and offspring BMI at 3 years of age, while taking several pre-and postnatal factors into account.

DESIGN: The Norwegian Mother and Child Cohort Study is a population-based pregnancy cohort study of women recruited from all geographical areas of Norway.

SUBJECTS: The study includes 31 169 women enrolled between 2000 and 2009 through a postal invitation sent to women at 17-18 weeks of gestation. Data collected from 5898 of the fathers were included. MAIN OUTCOME MESURES: Offspring BMI at 3 years was the main outcome measured in this study.

RESULTS: Mean maternal pre-pregnancy BMI was 24.0 kg m(-2) (s.d. 4.1), mean GWC in the first 30 weeks of gestation was 9.0 kg (s.d. 4.1) and mean offspring BMI at 3 years of age was 16.1 kg m(-2) (s.d. 1.5). Both maternal pre-pregnancy BMI and GWC were positively associated with mean offspring BMI at 3 years of age. Pre-pregnancy BMI and GWC also interacted, and the strength of the interaction between these two factors was strongly associated with the increase in offspring BMI among mothers who gained the most weight during pregnancy and had the highest pre-pregnancy BMI. Our findings show that results could be biased by not including pre-pregnant paternal BMI.

CONCLUSION(S): This large population-based study showed that both maternal pre-pregnancy BMI and GWC were positively associated with mean offspring BMI at 3 years of age.