Fetuses react to smell and taste in womb reveal four-dimensional ultrasound scans

UK: According to a new study conducted by UK researchers four-dimensional ultrasound scans show evidence that fetuses at 32 to 36 weeks react positively or negatively to smell and taste.

Scientists have recorded the first direct evidence that babies react differently to various smells and tastes while in the womb by looking at their facial expressions.

Researchers looked at how the fetuses reacted to either carrot or kale flavors just a short time after the flavors had been ingested by the mothers. Fetuses exposed to carrot showed more "laughter-face" responses while those exposed to kale showed more "cry-face" responses.

Their findings could further our understanding of the development of human taste and smell receptors. The researchers also believe that what pregnant women eat might influence babies' taste preferences after birth and potentially have implications for establishing healthy eating habits.

The study is published in the journal Psychological Science. Humans experience flavor through a combination of taste and smell. In fetuses, it is thought that this might happen through inhaling and swallowing the amniotic fluid in the womb.

Lead researcher Beyza Ustun, a postgraduate researcher in the Fetal and Neonatal Research Lab, Department of Psychology, Durham University, said:

"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.

"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.

"It was really amazing to see unborn babies' reaction to kale or carrot flavours during the scans and share those moments with their parents."

The research team, which also included scientists from Aston University, Birmingham, UK, and the National Centre for Scientific Research-University of Burgundy, France, scanned the mothers, aged 18 to 40, at both 32 weeks and 36 weeks of pregnancy to see fetal facial reactions to the kale and carrot flavours.

Mothers were given a single capsule containing approximately 400mg of carrot or 400mg kale powder around 20 minutes before each scan. They were asked not to consume any food or flavoured drinks one hour before their scans.

The mothers also did not eat or drink anything containing carrot or kale on the day of their scans to control for factors that could affect fetal reactions.

Facial reactions seen in both flavour groups, compared with fetuses 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.

Co-author Professor Nadja Reissland, head of the Fetal and Neonatal Research Lab, Department of Psychology, Durham University, supervised Beyza Ustun's research. She said:

"Previous research conducted in my lab has suggested that 4D ultrasound scans are a way of monitoring fetal 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 fetal abilities to sense and discriminate different flavours and smells from the foods ingested by their mothers."

Co-author Professor Benoist Schaal, of the National Centre for Scientific Research-University of Burgundy, France, said:

"Looking at fetuses' facial reactions we can assume that a range of chemical stimuli pass through maternal diet into the fetal 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.

Reference:

Ustun, B., Reissland, N., Covey, J., Schaal, B., & Blissett, J. (2022). Flavor Sensing in Utero and Emerging Discriminative Behaviors in the Human Fetus. Psychological Science, 0(0). https://doi.org/10.1177/09567976221105460