Prenatal thumb sucking is related to postnatal handedness.

This study followed-up 75 individuals who were observed sucking their thumb as fetuses and examined their handedness, assessed by a modified version of the Edinburgh Handedness Inventory, at 10-12 years of age. Of 60 right-handed fetuses, all were right-handed postnatally; 10 of 15 left-handed fetuses were left-handed and five right-handed. Male left thumb sucking fetuses were more likely to be right-handed children than females. The study indicates that the prenatal exhibition of lateralised motor behaviour, in this case thumb sucking, is indeed related to postnatal handedness, perhaps more strongly for right 'handed' fetuses than left 'handed' fetuses.