Washington – Scientists have discovered the first direct evidence that babies react differently to different smells and tastes while in the womb by observing their facial expressions.
A study led by Durham University's Fetal and Neonatal Research Lab, UK, took 4D ultrasound scans of 100 pregnant women to see how their unborn babies responded after being exposed to flavours from foods eaten by their mothers.
Researchers looked at how the foetuses reacted to either carrot or kale flavours just a short time after the flavours had been ingested by the mothers.
Foetuses 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 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.
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 foetal 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 foetal reactions.
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.
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 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, of the National Centre for Scientific Research-University of Burgundy, France, said:
"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.
Research co-author Professor Jackie Blissett, of Aston University, said: “It could be argued that repeated prenatal flavour exposures may lead to preferences for those flavours experienced postnatally. 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."