Smel­ling in utero

Did you know that the sense of smell is one of the first senses to be fully functional in the fetus? We can smell well before we are born, and our first olfactory preferences are forged in our mother’s womb !

In the late 1990s, researchers started to document the ability of the human fetus to perceive odors in utero. We know now that the olfactory system starts to form early in the first trimester. The olfactory system starts to be visible after just 9 weeks, when the fetus weighs only 2 grams, and from the 6th month of pregnancy the baby starts perceiving and memorizing smells through the amniotic fluid.

In adults, odorant molecules are carried by the breath into the nasal cavity where the olfactory mucosa is located. There, our olfactory neurons are in direct contact with the environment, only protected by a watery gel called mucus. For us to detect them as smells, molecules have to pass through this gel, which means that, contrary to popular beliefs, smells do travel through liquids and not only through air. That is why the amniotic fluid can easily carry smells to the olfactory mucosa of the fetus.

The mother’s diet influences olfactory and gustatory preferences before the baby is even born – but also after, through breastfeeding. Some aromas – such as garlic, cumin, fennel, curry, carrot, cheese, etc. – are particularly easily transferred from the mother to the fetus. After a few weeks of repeated exposure to certain elements consumed by the mother, the fetus will thus develop its first olfactory preferences. Olfactory responsiveness was for example assessed in neonates born to mothers who had or had not consumed anise flavor during their pregnancy. Both groups of infants were then followed-up for behavioral markers of attraction and aversion when exposed to anise odor and infants born to anise-consuming mothers showed a stable preference for anise odor in the first few days of their lives. 

A newborn baby is also able to recognize their mother by the smell of her skin and breast milk long before they can fully recognize her face, as their vision is not yet well developed. As the child grows however, olfactory sensitivity tends to decrease if not trained, which is why an education to smells isn’t something to overlook as a parent or an educator!

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