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 andχ^(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 152961 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<0.001).BMI category was also positively associated with unemployment(35%in obese class III vs 22%in normal BMI category)(p<0.001).Higher BMI categories were associated with increased rate of comorbidities,including hypertension(normal BMI:1.8%vs obese III:12.4%),diabetes mellitus(normal BMI:0.04%vs obese III:1.29%)and mental ill-health(normal BMI:5.0%vs obese III:11.8%)(p<0.001).Prevalence of maternal obesity varied with deprivation(most deprived:22.8%vs least deprived:15.7%)(p<0.001).Low BMI was associated with age<20 years,nulliparity,unemployment and mental ill-health(p<0.001).Conclusions The prevalence of maternal BMI>25 kg/m^(2)is increasing over time in Northern Ireland.Women are entering pregnancy with additional comorbidities likely to impact their life course beyond pregnancy.This highlights the need for prioritisation of preconception and inter-pregnancy support for management of weight and chronic conditions.