Babies observed reacting to taste and smell in the womb

Humans experience flavour through a combination of taste and smell; in foetuses, it is thought that this might happen through inhaling and swallowing the amniotic fluid in the womb. Now, scientists claim to have recorded the first direct evidence that foetuses react differently to various smells and tastes by observing their facial expressions.

Researchers from Durham University’s Fetal and Neonatal Research Lab took 4D ultrasound scans of 100 pregnant women to see how their unborn babies responded after being exposed to flavours consumed by their mothers. The research team, which also included scientists from Aston University and the French National Centre for Scientific Research (CNRS) at the University of Burgundy, scanned the mothers at both 32 and 36 weeks of pregnancy to see how the foetuses reacted to either carrot or kale flavours.

Facial reactions seen in both flavour groups, compared with foetuses in a control group who were not exposed to either flavour, showed that exposure to just a small amount of carrot or kale flavour was enough to stimulate a reaction. Foetuses exposed to carrot showed more ‘laughter-face’ responses, while those exposed to kale showed more ‘cry-face’ responses. The results were published in the journal Psychological Science.

“A number of studies have suggested that babies can taste and smell in the womb, but they are based on post-birth outcomes while our study is the first to see these reactions prior to birth,” said lead researcher Beyza Ustun, a postgraduate researcher at Durham University.

“As a result, we think that this repeated exposure to flavours before birth could help to establish food preferences post-birth, which could be important when thinking about messaging around healthy eating and the potential for avoiding ‘food fussiness’ when weaning.”

Co-author Professor Nadja Reissland, Head of the Fetal and Neonatal Research Lab, supervised Ustun’s work. She said, “Previous research conducted in my lab has suggested that 4D ultrasound scans are a way of monitoring foetal reactions to understand how they respond to maternal health behaviours such as smoking, and their mental health including stress, depression and anxiety.

“This latest study could have important implications for understanding the earliest evidence for foetal abilities to sense and discriminate different flavours and smells from the foods ingested by their mothers.”

Co-author Professor Benoist Schaal, from CNRS at the University of Burgundy, added, “Looking at foetuses’ facial reactions, we can assume that a range of chemical stimuli pass through maternal diet into the foetal environment.

“This could have important implications for our understanding of the development of our taste and smell receptors, and related perception and memory.”

The researchers say their findings might also help with information given to mothers about the importance of taste and healthy diets during pregnancy. They have now begun a follow-up study with the same babies post-birth to see if the influence of flavours they experienced in the womb affects their acceptance of different foods.

“It could be argued that repeated prenatal flavour exposures may lead to preferences for those flavours experienced postnatally,” said co-author Professor Jackie Blissett, of Aston University. “In other words, exposing the foetus to less ‘liked’ flavours, such as kale, might mean they get used to those flavours in utero.

“The next step is to examine whether foetuses show less ‘negative’ responses to these flavours over time, resulting in greater acceptance of those flavours when babies first taste them outside of the womb.”

Image caption: A 4D scan image of a foetus shows a laughter-face reaction after being exposed to the carrot flavour.

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