Triplets, birthweight, and handedness

Kauko Heikkilä*, Catharina E.M. Van Beijsterveldt, Jari Haukka, Matti Iivanainen, Aulikki Saari-Kemppainen, Karri Silventoinen, Dorret I. Boomsma, Yoshie Yokoyama, Eero Vuoksimaa

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

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The mechanisms behind handedness formation in humans are still poorly understood. Very low birthweight is associated with higher odds of left-handedness, but whether this is due to low birthweight itself or premature birth is unknown. Handedness has also been linked to development, but the role of birthweight behind this association is unclear. Knowing that birthweight is lower in multiple births, triplets being about 1.5 kg lighter in comparison with singletons, and that multiples have a higher prevalence of left-handedness than singletons, we studied the association between birthweight and handedness in two large samples consisting exclusively of triplets from Japan (n = 1,305) and the Netherlands (n = 947). In both samples, left-handers had significantly lower birthweight (Japanese mean = 1,599 g [95% confidence interval (CI): 1,526–1,672 g]; Dutch mean = 1,794 g [95% CI: 1,709–1,879 g]) compared with right-handers (Japanese mean = 1,727 g [95% CI: 1,699–1,755 g]; Dutch mean = 1,903 g [95% CI: 1,867–1,938 g]). Within-family and between-family analyses both suggested that left-handedness is associated with lower birthweight, also when fully controlling for gestational age. Left-handers also had significantly delayed motor development and smaller infant head circumference compared with right-handers, but these associations diluted and became nonsignificant when controlling for birthweight. Our study in triplets provides evidence for the link between low birthweight and left-handedness. Our results also suggest that developmental differences between left- and right-handers are due to a shared etiology associated with low birthweight.

Original languageEnglish
Pages (from-to)895-902
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number23
Early online date14 May 2018
Publication statusPublished - 5 Jun 2018


  • Birthweight
  • Handedness
  • Laterality
  • Prenatal development
  • Triplets

Cohort Studies

  • Netherlands Twin Register (NTR)


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