Adriëtte Oostvogels

80 Chapter 3 pBMI was based on prepregnancy height and weight as reported in the pregnancy questionnaire. In the whole ABCD cohort missing values were imputed maternal height (1.8% missing in the current study population) and prepregnancy weight (8.2% missing in the current study population) by a random imputation procedure using linear regression analysis and other variables known to be associated with maternal height and weight, respectively. 19 Child measurements Trained research assistants performed the health check for the 5-year-old children. The physical measurements included height, weight, and waist circumference. Height was determined to the nearest millimetre using a Leicester portable height measure (Seca, Hamburg, Germany) and weight to the nearest 100 g using a Marsden MS-4102 weighing scale (Oxfordshire, United Kingdom). Waist circumference was measured midway between the costal border and the iliac crest to the nearest millimetre using a Seca measuring tape. Fat mass was measured by arm-to-leg bioelectrical impedance analysis (Bodystat 1500 MDD machine (Bodystat Inc, Douglas, UK)). Definitions of measurements Outcome measures were the anthropometric measurements of the child at age 5–6 years and the lipid profile of the mother during early pregnancy. BMI was calculated as the child’s weight in kilograms divided by their height in meters squared. We also computed the waist-to-height ratio (WHtR); during the analysis WHtR was multiplied by 100. Fat percentage was based on calculations from our validation study. 20 Because the ApoB/ApoA1 ratio is a reliable predictor of heart disease, 21 we computed this ratio to evaluate its influence on adiposity of the child. BMI of the child was analysed as a dichotomous outcome value (overweight yes/no) defined according to the International Obesity Task Force guidelines. 22 Covariables The following covariables related to the mother were taken into account: maternal age (continuous), parity (primiparous yes or no), maternal height (continuous), hypertension (no hypertension, pre-existing or pregnancy induced), ethnicity (country of birth, Western/non-Western), smoking during pregnancy (smoker/non- smoker), alcohol use during pregnancy (drinker/non-drinker) and years of education after primary school (continuous). Maternal characteristics were self-reported in the pregnancy questionnaire, except for hypertensive status which was obtained by