A Study of Two Large Birth Databases Hints at Probable Causes for Left-handedness

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A team of researchers from Japan, the Netherlands, and Finland has discovered a connection between low baby birth weight and left-handedness. In the paper that has been published on Proceedings of the National Academy of Sciences, the team of researchers has elaborated on their study of two large birth datasets and what they have discovered from there.

Handedness Develops in Fetuses as Young as 10 weeks

Prior research has made a suggestion of a possible link between left-handedness and low birth weight. There have also been studies that suggest that handedness develops before even before one takes birth when fetuses are as young as 10 weeks. It has been seen exhibiting a preference for one thumb or the other on sonograms. In this new effort, the researchers sought to garner more evidence pertaining to the birth weight and handedness. To that end, they have obtained birth datasets from different countries, one from the Netherlands and the other one from Japan. Noting that earlier research has demonstrated that left-handedness is more common in twins, and even more common in triplets, the researchers made a choice on focusing their study exclusively on triplets. After filtering for triplets who were born at 33 weeks, the researchers pared down the datasets to 947 triplets from the one that was from the Netherlands and 1,305 from the one in Japan.

The researchers discovered that there is a difference between average birth weight between left and right handers, for the Dutch database it was 1.79 kg on average for lefties as compared to 1.903 kg for right-handers. The outcome for the Japanese babies was also quite similar, 1.599 kg for lefties and 1.727 kg for right-handers. They also noted also that the mother’s did not seem to make any noticeable difference, nor did the order of birth. The researchers also made a discovery that those babies born left-handed were comparatively slower to reach major motor-skill milestones such as standing, sitting, and crawling.

The researchers, however, point out that their results do not indicate that only low birth weight is the actual cause of left-handedness.

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