Ethnic differences in body mass index trajectories from 18 years to postpartum in a population-based cohort of pregnant women in Norway

Objectives: To explore ethnic differences in changes in body mass index (BMI) from the age of 18 years to 3 months postpartum. Design: A population-based cohort study. Setting: Child Health Clinics in Oslo, Norway. Participants: Participants were 811 pregnant women (mean age 30 years). Ethnicity was categorised into six groups. Primary outcome measures: The outcome variable was BMI (kg/m2) measured at the age of 18 and 25 years, at prepregnancy and at 3 months postpartum. Body weight at 18 years, 25 years and prepregnancy were self-reported in early pregnancy, while body height and weight at 3 months postpartum were measured. The main statistical method was generalised estimating equations, adjusted for age. The analyses were stratified by parity due to ethnicity×time×parity interaction (p