Adriëtte Oostvogels

6 effects of maternal pBMI found in this study would probably still be present when paternal pBMI was taken into account. Third, we ignored uncertainty of the estimated Box-Cox transformation parameters, however, since our data did not show high skewness, we assumed that the bias in the parameter estimates was sufficiently small to be ignored. 27 Finally, our study sample was older, more often of Dutch origin and higher educated than the mothers lost to follow-up. Because both mothers and their offspring lost to follow-up have more often overweight, true effects could be underestimated. A similar study to ours compared BMI growth patterns for different categories of both maternal and paternal BMI, but only up to age 3.5 years. 9 They also found that BMI growth patterns of obese mothers differed from the normal weight and overweight mothers, but in contrast to our study, no differences were found between growth of children of normal weight and overweight mothers. 9 Other studies did not study growth patterns per parental BMI group. 6-8,28 Although these studies found an effect of maternal BMI on weight and/or BMI of the child, no effect on height was shown, 6,7 or studied. 8,28 Growth is an interplay of genetic and environmental factors. 29 In twin studies, variability in weight and height at birth up to age 12 years is mostly determined by common environmental factors. 29 We found that growth patterns already differed at birth, which indicates that intra-uterine influences play a role. According to the overnutrition hypothesis, maternal overweight increases the transfer of glucose, free fatty acids and amino acids to the developing foetus. 30,31 This results in children with high birth weight and permanent changes in energy metabolism and adipose tissue, affecting postnatal weight and height growth. 32-34 Moreover, maternal overweight could alter offspring’s appetite control systems, resulting in overeating and increased weight and height gain. 35 In addition postnatal environment may explain part of the growth patterns found. Overweight and obese mothers have different infant feeding patterns, also in our cohort, 15-17,36 thereby increasing weight and BMI in infancy and the risk of overweight and obesity in childhood. 37,38 Furthermore, other postnatal factors might play a role: overweight and obese mothers often have more unhealthy eating habits and increased nutrient intake, with that increasing their offspring’s nutrient intake and their offspring’s weight as well. 36,39,40 In the present study, maternal obesity seemed to affect growth patterns of weight in girls more than in boys. This is in contrast to the study of Andres et al, 28 but in agreement with Botton et al. who showed a stronger (non-significant) effect of maternal BMI on girls’ weight growth velocity than on boys’. 7 There is some evidence for sex differences in sensitivity to obesogenic environmental exposures, girls born 159 pBMI and offspring’s growth patterns