Behavioral and Heart Rate Pattern Differences Between Breast-Fed and Bottle-Fed Neonates

Behavioral and physiological differences between 61 breast-fed and 39 bottle-fed neonates were assessed between 17 and 56 hr postpartum (M age = 37 hr). Ten minutes of baseline heart rate pattern and respiration data were recorded during sleep, and the Neonatal Behavioral Assessment Scale (NBAS) was administered subsequently. Perinatal and demographic information was collected by maternal interview and delivery records. Results indicate that breast-fed infants had significantly longer heart periods, elevated heart period variability, and higher vagal tone than bottle-fed infants. Behaviorally, breast-fed infants were significantly more irritable, more difficult to console, and more often unable to complete the alert orientation portion of the assessment. These results could not be attributed to perinatal status or maternal variables. These findings suggest that breast-feeding is associated not only with more optimal physiological organization in the early neonatal period, but also with increased irritable reactivity. The relevance of several nutritional and interactional factors is evaluated. The data indicate that method of feeding should be considered an important dimension in studies of neonatal functioning.