Olfaction

Pre- and Postnatal Olfaction

Biological development of the fetus is such that by 7 months it is probably able to detect chemicals present in the mother’s amniotic fluid. This advance is suggested by the presence of olfactory detection abilities in preterm neonates, by findings from animal research and from intriguing amniotic scenting experiments conducted in humans. In the latter, mothers ingest anise approximately 2 weeks before the baby is due to be born. Anise, alongside vanilla, garlic, and several other food-related odors, can result in distinctly scented amniotic fluid. Babies exposed to anise in utero show a preference for this odor on test, turning [Page 1545]their head more toward an anise-scented pad than nonexposed babies. Although many studies have indicated that newly born babies can detect a range of different odors (established using a range of techniques, including behavioral [e.g., habituation, facial changes] and physiological [e.g., electroencephalogram]), it is the neonate’s reaction to food and comfort-related smells that has been a particular focus of attention. Both 2-week-old breastfed and bottle-fed babies orient to the odor of a lactating mother’s breast pad, over that of the breast pad of a nonlactating mother, a formula scented pad, or an unscented pad. Whether this preference is innate or a consequence of learning is unresolved. A similar behavior has been studied in rabbits, where there appears to be a mammary pheromone, the purpose of which is to trigger breast seeking and suckling in the pup. In humans, a mammary pheromone is possible; however, a preference for breast-related smells could equally be achieved by some commonality of scent between amniotic fluid, the breast, and breast milk. However, the finding that both breast- and bottle-fed neonates will readily turn and move toward the scent of another mother’s breast suggests a common chemical cue that either all neonates have been exposed to or one that all are hardwired to prefer. The study of this topic is practically significant as these findings are being used to aid feeding in preterm babies.

...