Adriëtte Oostvogels

Methods Study population The present study is part of the Amsterdam Born Children and their Development (ABCD) study, a population-based, prospective, longitudinal birth cohort with the main goal to examine and determine factors in early life that might explain the later health of the child, and differences in health between children (www.abcd-study. nl). The design of the study has been described previously. 19 The present study was conducted according to 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 participants. In brief, between January 2003 and March 2004 12373 pregnant women in Amsterdam were approached at their first antenatal visit to an obstetric caregiver (median 13 weeks; IQR=12-14 weeks) to participate in the study. Of this group, 8266 (response rate 67%) women filled out the pregnancy questionnaire and we had growth data available of 5558 of their children from the Amsterdam Youth Health Care registration (YHC). This registration contains growth data, date of delivery, sex, birth weight, and gestational age of all children. 19 Twins, preterm-born children (<37 weeks of gestation), children of underweight mothers (BMI <18.5 kg/m 2 ), children with congenital anomalies, children with ≤ 3 growth measurements and cases with missing data on covariates were excluded. The final study sample consisted of 3508 children (Figure 1). Prepregnancy BMI Prepregnancy BMI was based on height and weight as reported in the pregnancy questionnaire. Maternal pBMI was divided into three categories based on the WHO guidelines: normal weight (≥18.5-25 kg/m 2 ), overweight (≥25-30 kg/m 2 ), and obesity (≥30 kg/m 2 ). 20 Growth data Growth data were obtained from the YHC of the Public Health Service in Amsterdam. Following a standard procedure, at regular follow-up moments between birth and age 7 years, trained nurses measured weight (mean=12.7 times, SD=2.6) and height (mean=11 times, SD=2.3). 150 Chapter 6