Handedness and birth weight

A study finds a link between low birth weight and left-handedness in two large sets of Japanese and Dutch newborn children. As early as 10 weeks of gestation, when growing human fetuses begin moving their arms, the question of whether the newborn will be left-handed, right-handed, or ambidextrous is addressed. Previous studies have suggested direct links between left-handedness and low birth weight (less than 1.5 kg). Because newborn triplets are around 1.5 kg lighter than singletons, Kauko Heikkilä and colleagues examined links between birth weight and handedness in two large datasets composed of 1,305 triplets from Japan and 947 triplets from the Netherlands of average gestational age of around 33 weeks. Whereas the average birthweight of left-handers in the Japanese sample was 1.599 kg, right-handers weighed 1.727 kg on average. Similarly, left-handers in the Dutch sample weighed 1.794 kg on average, compared with the average birth weight of 1.903 kg for right-handers. Analysis within and between families also suggested a link between left-handedness and low birth weight, regardless of maternal or gestational age. By contrast, handedness appeared to be unrelated to birth order in both samples. In the Japanese sample, left-handers reached motor milestones significantly later compared with right-handers; the authors observed no such association in the Dutch sample. Though the study did not account for maternal stress, birth complications, or fetal focal brain injuries, it reinforces the link between left-handedness and low birth weight using a large triplet data set, according to the authors.

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Article #17-19567: "Triplets, birthweight, and handedness," by Kauko Heikkilä et al.

MEDIA CONTACT: Kauko Heikkilä, University of Helsinki, FINLAND; tel: +358400244389; e-mail: <kauko.heikkila@helsinki.fi>; Eero Vuoksimaa, University of Helsinki, FINLAND; e-mail: <eero.vuoksimaa@helsinki.fi>