The goal of the study was to investigate some of the factors suspected to be related to children's handedness: presentation during the last weeks of gestation and at birth (cephalic or breech), side of presentation (right or left), number of weeks of gestation, season of birth, parents' handedness and sex. We analyzed the relationships between these factors and the child's handedness at five years. Children (n = 1897) from the EDEN cohort participated in the study, among which 1129 were tested for handedness at five. The father's handedness, but not the mother's, was significantly related to the child's hand preference. The percentage of left-handed children was significantly larger when the father was non-right-handed compared to right-handed, and tended to be larger among children in non-left-cephalic presentation compared to left-cephalic presentation. Girls, but not boys, were significantly less lateralized when they were born before 37 weeks of pregnancy than after. Finally, children born in winter or spring were slightly but significantly less lateralized than children born in summer or autumn. All six children who were not lateralized at 5 presented one or several of these factors. These results are discussed in light of the mixed model of handedness.
Keywords: family handedness; handedness; prenatal factors.