As measures of weight-for-height, ponderal index at birth was calculated as birth weight/birth length3 (kg/m3), and body mass index (BMI) was calculated as weight/height2 (kg/m2) in the children at age 9 y and in the mothers pre-pregnancy. Fat mass was corrected for height by calculating the fat mass index fat mass / height2 (kg/m2) [18]. Truncal fat index was similarly calculated. Obesity was defined in mothers as BMI > 30 kg/m2, and in children as BMI > 97th percentile for sex and age by comparison with the UK 1990 growth reference [19]; use of different cutoffs produced very similar risk scores (unpublished data).
