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. 17 In short: 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) and 8266 (67%) women filled out the pregnancy questionnaire (phase 1). Follow-up covered a questionnaire around 3 months after birth and the follow-up of growth from the Youth Health Care (YHC) centres (phase 2). In 2008 the third phase of the study started with retrieving the addresses of 6161 mothers from the YHC and sending them a questionnaire, including an informed consent form for the health check, which was returned by 4488 (73%) of the participants. 3321 children aged 5-6 years (2008–2010; mean age: 5.7±0.5 years) participated in the health check and, in a subsample of 2003 children, blood samples were drawn (phase 3). Multiple births were excluded preceding the third phase. We included only children of whom growth data were available (n=1636) and who had valid values for the metabolic components. Children with congenital anomalies, non- fasting blood samples and children born from mothers with diabetes were excluded. The final sample for this study consisted of 1459 children (Figure 1). The present study was conducted according to the guidelines laid down in 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. Prepregnancy BMI Prepregnancy BMI was based on height and weight as reported in the pregnancy questionnaire. Missing values were imputed for maternal height (1.9% missing) and prepregnancy weight (7.7% missing) by a random imputation procedure using linear regression analysis and other variables known to be associated with maternal height and weight. 18 Maternal pBMI was used continuously as well as dichotomously: no overweight <25 kg/m 2 or overweight/obese ≥ 25 kg/m 2 . 178 Chapter 7