Small body size at birth and behavioural symptoms of ADHD in children aged five to six years

Background: Behavioural disorders with a neurodevelopmental background, such as attention deficit hyperactivity disorder (ADHD), have been associated with a non-optimal foetal environment, reflected in small body size at birth. However, the evidence stems from highly selected groups with birth outcomes biased towards the extreme low end of the distribution in birth weight. Whether a similar association exists among the normal range of term birth is unclear. Methods: The ADHD Rating Scale was filled in by the biological mothers and fathers of children aged five to six years who were born healthy at term. Information on weight (kg), height (cm), head circumference (cm), and gestational age at birth were obtained from hospital records, and the ponderal index (kg/m(3)), a commonly used measure of thinness, and head circumference-to-length ratio were calculated. Results: Behavioural symptoms of ADHD were predicted by a lower ponderal index, a smaller head circumference, and a smaller head circumference-to-length ratio (beta's: -.12 to -.14, p's < .05). Adjustments for length of gestation, mother's age, tobacco and alcohol use during pregnancy, pre-pregnancy body mass index (BMI), or parity, the monthly gross income of the family, child's BMI at the age of five to six years or gender did not change the associations. Results: These results suggest that physiological adaptation in utero, indicated by small body size at birth, within term gestational range may increase the susceptibility to behavioural symptoms of ADHD.