Soothing effect of amniotic fluid smell in newborn infants.

Newborn young of several mammalian species are attracted to the odor of amniotic fluid (AF); these chemical cues also appear to calm neonates and help them adapt to their novel postnatal environment. AF odor likewise elicits positive (head orientation) responses by human infants. The present study systematically examined whether the odors of AF and mother's breasts influence the crying of the newborn infant, when separated from its mother. The total crying time from 31-90 min postnatal was registered on tapes in 47 healthy fullterm newborns, allocated to one of three conditions; exposure to either AF or breast odor or no exposure (controls). Babies exposed to AF smell cried significantly less (median 29 s) than babies in the two other groups (breast odor--301 s, controls--135 s). The data are consistent with the hypothesis that the fetus may become familiar with chemical cues present in the intrauterine environment. Our data provide new evidence of the human baby's fine olfactory discrimination capacity, and add to the growing body of evidence indicating that naturally occurring odors play an important role in the mediation of infants' early behavior.