Left-handedness is caused by both genetic and non-genetic factors.

One factor that has been discussed to affect handedness in children is post-traumatic stress in mothers.

A new study investigated the effect of post-traumatic stress in mothers on handedness in toddlers.

Higher post-traumatic stress in mothers during pregnancy was linked to higher mixed-handedness in children.

What are the causes of left-handedness?

What causes someone to be left-handed, mixed-handed, or right-handed? It is well-known that genetics has a substantial influence. Children of two left-handed parents are more likely to be left-handed themselves than children of two right-handed parents.

But genetics is not the whole story. Studies have shown that several factors before and during birth and during early life also influence whether someone becomes left-handed or not. For example, handedness is influenced by breastfeeding, birthweight, season of birth, and being part of a multiple birth (De Kovel et al., 2019). A factor that has also been discussed to affect handedness is maternal stress, but it has so far not been investigated well in psychological studies.

A new study on stress before birth in mothers and handedness in their children

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