Pre- and post-natal factors and physical activity in childhood: The Norwegian Mother, Father and Child Cohort study.

Few studies have examined the possibility that pre- and post-natal factors may be non-linearly associated with later physical activity. We used data from the Norwegian Mother, Father and Child Cohort study (MoBa) and the Medical Birth Registry of Norway (MBRN), including 48 672 children with available data on leisure time physical activity (LTPA) at child's age 7 years. Restricted cubic and linear splines or linear regression was used to examine the associations between maternal pre-pregnancy BMI, birth weight for gestational age, and infant weight gain from birth to 1 year with LTPA (frequency/wk) in 7-year-old children. The results suggest no associations between maternal pre-pregnancy BMI, birth weight, and infant weight gain on subsequent LTPA in girls. Maternal pre-pregnancy BMI and birth weight may be non-linearly associated with LTPA in 7-year-old boys. Infant weight gain (change in weight z-score from birth to 1 year) may be weakly linearly associated with LTPA in boys. Pre- and post-natal factors may therefore influence LTPA in childhood differently in boys and girls. Maternal pre-pregnancy BMI and birth weight are positively associated with LTPA at the lower ends of the maternal pre-pregnancy BMI and birth weight continuums in boys. The negative associations at the higher ends of the continuums and the positive association between infant weight gain and LTPA in boys may not be important and needs further replication.