Adriëtte Oostvogels

8 199 Growth patterns to overweight Introduction Over the past decades there has been a worldwide increase in the prevalence of overweight and obesity among children. 1 Children with overweight or obesity are at increased risk of adult overweight and its associated comorbidities. 2-5 Early prevention of childhood overweight is therefore of absolute importance and identifying critical periods in the development of childhood overweight is an essential step towards effective prevention. BMI growth patterns differ from early age onwards between children who will develop overweight in late childhood compared to those with normal weight. 6-8 Children with overweight have higher birth weights, and faster rates of growth in the first years of life. 6-11 Moreover, their BMI peak tends to be higher and their adiposity rebound – a renewed rise in BMI after the decrease in BMI that followed the BMI peak – tends to be earlier with a steeper increase in BMI compared to those of normal weight. 6,7,12-14 This general pattern to overweight is likely to reveal differences when comparing lower versus higher socioeconomic groups, or ethnic minority populations versus the host populations. Although this has not been studied directly, previous studies provide indications to suggest such differences in growth patterns. For instance, children of low socioeconomic background are born smaller, and are more likely to be overweight at age 5 years, 15,16 showing an increased growth in the first years compared to children of high socioeconomic background. In addition, children in ethnic minority populations are more often small at birth, but are more overweight in childhood compared to children from Dutch origin. 17-20 This shows that they grow faster after birth , compared to children of Dutch origin. There are indications that these differences in early postnatal growth are partly due to ethnic and socioeconomic differences in feeding practices. 21-27 Therefore, this study will investigate BMI growth patterns to overweight at age 5-6 years using longitudinal measurements of BMI from birth onwards stratified for maternal ethnic origin and maternal socioeconomic background. Ethnic origin will be indicated by country of birth (European origin versus non-European origin) and socioeconomic background by maternal educational level. Growth curves will be described for boys and girls separately, as growth patterns of boys and girls have been shown to differ. 28,29 Ethnic or socioeconomic disparities in timing of the critical periods in BMI growth to overweight could help to better identify children in minority groups at risk for childhood overweight at an early stage of development.