The occurrence rate and correlation factors of thumb-in-palm posture in newborns.

Bilateral fisting of hands, including adduction and infolding of the thumbs (cortical thumbs), is an expected finding in term infants. Clinically, the cortical thumb position is a transient and normal, but not general, hand posture in newborns. The aim of this study was to analyze the rate of occurrence and the factors possibly affecting the cortical thumb (thumb-in-palm) posture in term newborns. We enrolled 197 low-risk term newborns and observed the posture of their hands once daily from the day of birth for 3 consecutive days. The occurrence rates of the thumb-in-palm posture of the right hand on the first, second, and third days were 62.8%, 60.9%, and 50%, respectively, and those of the left hand were 60.3%, 55.8% and 53.2%, respectively. There was a significant reduction on a day-to-day basis in the right hand and an insignificant reduction in that of the left hand. Factors including sex, gestation age, birth weight, method of delivery, and alertness were analyzed, and no relationship was evident between these factors and the occurrence rates of the cortical thumb posture. Our observations suggest that the cortical thumb posture is indeed a predominant hand posture in our hospital, yet it is not a general phenomenon in all term newborns.