Triplets, birthweight, and handedness

Area of Science:

• Human development
• Neuroscience
• Genetics

Background:

• Handedness mechanisms remain unclear.
• Low birthweight and premature birth are linked to left-handedness, but causality is unknown.
• Multiple births, like triplets, have lower birthweights and higher left-handedness prevalence.

Purpose of the Study:

• To investigate the association between birthweight and handedness in triplets.
• To determine if low birthweight or prematurity is the primary factor in left-handedness.
• To explore the role of birthweight in developmental differences between left- and right-handers.

Main Methods:

• Analysis of two large triplet cohorts from Japan (n=1,305) and the Netherlands (n=947).
• Comparison of birthweight between left-handed and right-handed individuals within families.
• Statistical control for gestational age to isolate birthweight effects.

Main Results:

• Left-handers in both cohorts exhibited significantly lower birthweights compared to right-handers.
• Within-family analyses confirmed left-handedness is associated with lower birthweight, independent of gestational age.
• Delayed motor development and smaller head circumference in left-handers became non-significant when controlling for birthweight.

Conclusions:

• This triplet study provides strong evidence linking low birthweight to left-handedness.
• Developmental disparities observed in left-handers appear to be mediated by factors related to low birthweight.
• Low birthweight may be a key underlying factor influencing both handedness and early development.