Birth weight and handedness in boys and girls

The authors analysed handedness in association with birth weight for 1,387 boys and girls aged 5 to 10 years. Increased birth weight was significantly associated with right-handedness in boys and with left handedness in girls. In multiple regression models left handedness was significantly more common among boys and among children of better educated mothers and tended to decrease with age. The different association of birth weight and hand preference in boys and girls indicates that the prenatal hormonal factors that affect brain lateralisation and handedness are qualitatively or quantitatively different in the two sexes and may be differently associated with birth weight.