Relationship between heart rate indices of the orienting response and birth weight in normal full-term newborns.

The results of this study indicate that birth weight in normal term infants is related to changes in heart rate in response to auditory stimulation. Only infants above the median in birth weight responded to stimulus onset and offset. They exhibited a change in response to onset from a heart rate acceleration (defensive response) on the 1st trial to heart rate deceleration (orienting response) on later trials. The response to stimulus offset was a deceleration. Those infants below the median in birth weight showed no significant responses to onset or offset.