Weight change before and after the introduction of solids: results from a longitudinal birth cohort.

We studied the association, and its direction, between the introduction of solids and weight-for-height (WFH) change between birth and 45 months. Pregnant women were asked to participate in a birth cohort during their first antenatal visit. Data from 3184 children were used. The timing of the introduction of solids was reported by the mother from a questionnaire at 12 months postpartum, and categorised into very early (0-3 months), early (3-6 months) and timely (after 6 months) introduction of solids. Anthropometric data were collected during standardised child health centre visits. WFH was converted into a z-score. Repeated-measurements analyses with splines positioned according to the moments of solid introduction were used to obtain estimates for WFH change before and after the introduction of solids. Analyses were adjusted for educational level, ethnicity, smoking during pregnancy, mother's BMI, breast-feeding, history of food allergy and infant's hospital admission. Before solids were introduced, weight gain was higher in children introduced to solids early (z= 0.65, 95 % CI 0.34, 0.95) than in children introduced to solids very early (z= 0.02, 95 % CI -0.03, 0.08) and timely (z= -0.04, 95 % CI -0.05, -0.03). Shortly after the introduction of solids, children introduced to solids very early and early showed a relative decrease in WFH. WFH change did not differ between the solid introduction groups after 12 months, and at that time, weight change was as expected (i.e. z= 0). We therefore conclude that differences in WFH in childhood are not the result of early introduction to solids.