Role of prenatal position in grasp-reflex asymmetry in human neonates

Grasp-reflex strengths were quantitatively measured from the right and left hands of 70 full-term human neonates. The right-left grasp-reflex linearly correlated with grasp-reflex only of the right hand in neonates with a right-ear-facing-out prenatal position. In neonates with left-ear-facing-out prenatal position, this grasp-reflex linearly increased with the grasp-reflex of the right hand and linearly decreased with the grasp reflex of the left hand. It was suggested that grasp-reflex asymmetry in neonates may, at least partly, depend upon prenatal position, which may also influence the later developing hand preference in humans.