Attractiveness of amniotic fluid odor: evidence of prenatal olfactory learning?

Human infants are responsive to maternal odors beginning shortly after birth. In several non-human mammals, the fetus is capable of olfactory learning and in some species neonates are attracted to the odor of amniotic fluid (AF). The present study examined the responses of newborn babies to AF in a biologically relevant context, i.e. during their initial attempt to locate the mother's nipple/areola. We observed newborns' spontaneous choice between a breast with the nipple/areola moistened with AF and an untreated breast; 23 of 30 infants chose the AF-treated breast. All babies had been washed before the observations, and only 12/30 sucked their hands/fingers prior to approaching the nipple/ areola. In a previous study with unwashed newborns, the corresponding proportion was 27/30 (p < 0.001). We tentatively suggest that the observed attraction to AF odor may reflect fetal exposure to that substance (i.e. prenatal olfactory learning). Because of the salience of biological odors for neonates, products that eliminate or mask such cues should be avoided during the perinatal period.