Laughing at carrots, crying at kale: Depending on what the mother ate, unborn babies react with different facial expressions. This is now shown by a study using 4D ultrasound scans of almost 100 pregnant women. According to this, the fetuses perceive the aromas of the food eaten by their mother in the amniotic fluid and react accordingly. Further studies should clarify how prenatal imprinting contributes to taste preferences later in life.
Even in the womb, unborn babies get a lot of information about their outside world: they hear noises from their surroundings, perceive light stimuli through the abdominal wall and feel what is around them. The sense of smell and taste also develop early on: the fetuses indirectly taste their mother's food through flavoring substances dissolved in the amniotic fluid. Previous studies had already shown that unborn babies swallow more amniotic fluid when it was mixed with a sterile sugar solution. On the other hand, if the amniotic fluid was made bitter, the swallowing rate decreased.
Yuck, bitter!
A team led by Beyza Ustun from Durham University in England has now observed for the first time directly via ultrasound how fetuses react to different aromas from the mother's food. To do this, the researchers had 97 women in the 32nd week of pregnancy swallow either a capsule with carrot powder or a capsule with kale powder and observed the facial expression of the unborn baby in 4D ultrasound 20 minutes later. The team also repeated the study in 81 women in the 36th week of pregnancy.
The result: "Fetuses exposed to the taste of carrots showed a smile face more often, while fetuses exposed to the taste of kale showed more wine faces," the researchers report. 30 unborn babies who were not exposed to any aroma at the time of observation served as a comparison group. Facial expressions were similar at 32 and 36 weeks of gestation, with the older fetuses grimacing even more in response to the bitter taste of kale. "It was really amazing to see the unborn babies' reaction to the taste of kale or carrot during the scans and to share those moments with their parents," says Ustun.
The offspring eats with you
Ustun's colleague Nadja Reissland explains: "Previous research in my lab has shown that 4D ultrasound scans are a way to observe fetal responses to understand how they respond to maternal health behaviors and mental health, such as smoking , stress, depression and anxiety.” From her point of view, the current study could help to make it clear to expectant mothers how much the unborn child already gets from their diet.
"If we look at the facial responses of fetuses, we can assume that a range of chemical stimuli enter the fetal environment through the maternal diet," says co-author Benoist Schaal from the University of Burgundy in France. "This could have important implications for our understanding of the development of our taste and smell receptors and the associated perception and memory."
Getting used to it in the womb?
In a follow-up study already underway, the researchers want to use the same babies after birth to find out to what extent the flavors that the fetuses were exposed to in the womb influence the acceptance of different foods later in life. If this thesis is confirmed, it would support recommendations according to which pregnant women should eat as diverse a diet as possible in order to get their baby used to many different flavors before birth.
"One could argue that repeated prenatal taste exposures can lead to preferences for the postnatal taste experiences. In other words, exposing the fetus to less-loved flavors, such as kale, could mean that it becomes accustomed to those flavors in the womb,” explains co-author Jacqueline Blissett of Aston University in England. "The next step is to examine whether fetuses show fewer negative reactions to these flavors over time, leading to greater acceptance of these flavors when babies first taste them outside the womb."
Source: Beyza Ustun (Durham University, UK) et al., Psychological Science, doi: 10.1177/09567976221105460