Tracking of body size from birth to 7 years of age and factors associated with maintenance of a high body size from birth to 7 years of age – the Norwegian Mother and Child Cohort study (MoBa)

OBJECTIVE: To examine tracking of body size among children participating in the Norwegian Mother and Child Cohort Study (MoBa) from birth to 7 years of age and additionally to explore child and parental characteristics associated with maintenance of a high body size in this period of life. DESIGN: Anthropometric data at birth and at 1, 3 and 7 years of age were collected by questionnaires addressed to the mother. SETTING: Participants were recruited from all over Norway during the period 1999-2008. SUBJECTS: A total of 3771 children had complete anthropometric data at birth and at 1, 3 and 7 years of age; the sample includes children born between 2002 and 2004. RESULTS: Cohen's weighted kappa pointed to fair (0.36) to moderate (0.43) tracking of body size from birth to 7 years of age. Generalized estimating equations further indicated that children in the highest tertile of ponderal index at birth had nearly one unit higher BMI (kg/m(2)) at the age of 7 years compared with children in other tertiles of ponderal index at birth. Having parents with high BMI (≥ 25.0 kg/m(2)) increased the odds of having a stable high body size from birth to 7 years of age; moreover, girls had significantly higher odds compared with boys. CONCLUSIONS: The study indicates fair to moderate tracking of body size from birth to 7 years of age. From a public health perspective, early prevention of childhood overweight and obesity seems to be especially important among children of parents having a high BMI.