Trends in maternal body mass index in Northern Ireland: a cross-sectional and longitudinal study

OBJECTIVES: Explore (1) associations between maternal body mass index (BMI), demographic and clinical characteristics, (2) longitudinal trends in BMI, (3) geographical distributions in prevalence of maternal overweight and obesity. DESIGN: Retrospective population-based study. SETTING: Linked, anonymised, routinely collected healthcare data and official statistics from Northern Ireland. PARTICIPANTS: All pregnancies in Northern Ireland (2011-2017) with BMI measured at ≤16 weeks gestation. METHODS: Analysis of variance and χ(2) tests were used to explore associations. Multiple linear regression was used to explore longitudinal trends and spatial visualisation illustrated geographical distribution. Main outcomes are prevalence of overweight (BMI ≥25 kg/m(2)) and obesity (BMI ≥30 kg/m(2)). RESULTS: 152 961 singleton and 2362 multiple pregnancies were included. A high prevalence of maternal overweight and obesity in Northern Ireland is apparent (singleton: 52.4%; multiple: 48.3%) and is increasing. Obesity was positively associated with older age, larger numbers of previous pregnancies and unplanned pregnancy (p