Adriëtte Oostvogels

200 Chapter 8 Methods Study population This study was part of the Amsterdam Born Children and their Development (ABCD) study. The aim of the prospective cohort ABCD-study was to examine the association between maternal lifestyle, medical, psychosocial and environmental conditions during pregnancy and offspring’s health at birth as well as in later life. 30 Pregnant women in Amsterdam were approached at their first antenatal visit to an obstetric caregiver (median 13 weeks (IQR=14-16)) to participate. Of the 12373 women approached, 8266 filled out the pregnancy questionnaire. Of the mothers who gave birth to a live-born singleton, 6734 gave permission for follow-up. In the following years, the follow-up of growth of 5865 children was collected from files of the Youth Health Care registration of the Public Health Service in Amsterdam. Moreover, at age 5-6 years 3321 of the children participated in the ABCD health check, where weight and height were measured. Of the 4539 with known BMI at mean age 5.7 (SD=0.4) years, children born with congenital anomalies (n=105), celiac disease (n=6), underweight (n=511) or with missing growth data (n=203) were excluded, leaving 3714 children in the final study sample (Figure 1). For this study, ethical approval was obtained according to the guidelines of the Declaration of Helsinki, and all procedures involving human subjects were approved by the review boards of all Amsterdam hospitals and the Registration Committee of Amsterdam. Written informed consent was obtained from all subjects. BMI growth pattern Growth data were obtained from the Youth Health Care registration of the Public Health Service in Amsterdam. Following a standard procedure, trained nurses measured at regular follow-up moments between birth and age 7 years weight and height and BMI was calculated (mean=12.8; SD=3.1). For each child an individual BMI growth curve was modelled. 31 Since the length of the child was first measured at 4 weeks of age, the BMI score at birth was extrapolated. Overweight at age 5-6 years BMI was based on height and weight measures at 5-6 years old, obtained from the ABCD health check (69.4%) complemented by growth measurements of the Youth Health Care registration (30.6%). Height was measured to the nearest millimeter using a Leicester portable height measure (Seca), and weight to the nearest 100