Triplets, birthweight, and handedness

• Low birthweight is a risk factor for developmental delay, and is also associated with a higher odds of being left-handed. Likewise, compared with singletons, triplet births encompass an increased probability of left-handedness and developmental delay. In a large study, including triplets from two countries, we studied if left-handedness is associated with birthweight and postnatal development. Triplets have naturally low birthweights, being about 1.5 kg lighter than singletons. In both samples of triplets, we showed that left-handedness was associated with lower birthweight. Left-handers had also smaller infant head circumference and delayed motor development compared with right-handers, but these differences were not evident when controlling for birthweight.

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