Adriëtte Oostvogels

children grow slower than formula-fed peers. 34 Therefore, children of mothers with overweight/obesity could grow faster, because of the lack of exclusive breastfeeding. On the other hand, there are also indications that the composition of breasfeeding differs between women with normal weight and women with overweight/obesity, affecting offspring’s postnatal growth. A rodent cross-fostering study showed that pups suckled by obese dams had an increased risk of overweight later in life. 35 Nevertheless, in the present study, adjusting for breastfeeding did not change our results, what could be explained by our early postnatal period, since the largest differences in growth between breastfed and formula-fed children were observed in the period between 3-6 months. 36 Strengths and limitations The major strengths of the present study are the ability to combine both the impact of maternal pBMI and postnatal growth in a multi-ethnic cohort with a large sample size, serial measurements of postnatal growth, and biometric data collected by standardized protocols. Moreover, the availability of lifestyle factors during pregnancy and characteristics of the offspring allowed us to control for these important factors. However, we lack information on paternal BMI, which would have provided more information on the genetic and environmental factors a child is exposed to, nonetheless a recent study in a comparable cohort showed stronger associations with maternal than with paternal prepregnancy BMI. 6 Also the lacking of information on gestational weight gain during pregnancy, known to be associated with offspring’s cardiovascular risk factors independent of maternal pBMI, 8 could overestimate the true association. The study has some additional limitations: although we took care to prevent attrition, selection bias was observed. Our study population was less ethnically diverse and the mothers were more highly educated (a proxy for socioeconomic status), but no differences in maternal pBMI were observed. Since we know that Dutch children and children of high educated women have a healthier metabolic profile than non-Dutch children and children of low educated women in our cohort, 37-39 we assume that this study could have underestimated the effect of pBMI on offspring’s metabolic outcomes. Finally, maternal pBMI was self-reported in questionnaires; because women tend to overestimate their height and underestimate their weight, this could result in an underestimation of BMI. 40 However, since we used BMI as a continuous variable in the present study, this has little effect. 40 Moreover Gaillard et al. found that maternal self-reported prepregnancy weight and the woman’s measured weight at the rst antenatal clinic were highly correlated. 6 190 Chapter 7