Adriëtte Oostvogels

6 To test whether there were any statistically significant sex differences between the associations of the mother’s pBMI and the SD score, we fitted a second model to the data in the second stage without correction for sex specified as Z i  (t) = X i β + ƒ (t | pbmi i  ) + ϕ i + ε With an ANOVA, the fit of the two models was evaluated. Note that because our analysis is mainly of an exploratory nature, we report the differences between the pBMI groups separately for boys and girls. Differences between boys and girls were formally tested by adding the sex to the model and evaluating if this resulted in a significant improvement of the fit. To provide more insight when differences start to deviate, we reported the difference between the pBMI groups in weight, height and BMI on target ages. All analyses were performed with the statistical program R (R Development Core Team 2008). For the first stage of the analysis, we used the GAMLSS package. 23 The second stage of the analyisis was performed with the mgcv package. 25 Full model results are presented in supplementary table 5. Sensitivity analyses were performed in a more homogeneous sample containing the Dutch-only participants. Results Study population The current study population consisted of 3508 mother-child pairs (Figure 1). Compared to mothers who did not give permission to obtain growth data, or whose offspring’s growth data were not available (n=2576), mothers in the present study sample were older, slightly taller, slightly leaner, had a higher education level, were more often of Dutch origin, nulliparous, smoked less during pregnancy, but had more often hypertension in pregnancy and exclusively breastfed their child longer. No significant differences were found in diabetes during pregnancy and offspring’s sex (Supplementary Table S1). Of all mothers included in this study, 78.8% had a normal weight before pregnancy (n=2766), 15.4% had overweight and 5.8% had obesity. Compared to normal weight mothers before pregnancy, the overweight and obese mothers were more often of non-Dutch origin, less educated, more often multiparous, had more often had diabetes and hypertension during pregnancy and gave breastfeeding less often and for a shorter time period (Table 1). 153 pBMI and offspring’s growth patterns