(CNN) While it is known that some children are not huge fans of greens, a new study suggests that such dietary preferences could come about before they're even born.
Fetuses create more of a "laughter-face" in the womb when exposed to the flavor of carrots consumed by their mother and create more of a "cry-face" response when exposed to kale, according to a study published in the journal Psychological Science on Wednesday.
"We decided to do this study to understand more about fetal abilities to taste and smell in the womb," lead researcher Beyza Ustun, a postgraduate researcher in the Fetal and Neonatal Research Lab at Durham University in the UK, told CNN Thursday via email.
While some studies have suggested that babies can taste and smell in the womb by using post-birth outcomes, "our research is the first one showing direct evidence of fetal reactions to flavours in the womb," Ustun added.
"The findings shows that fetuses in the last 3 months of pregnancy are mature enough to distinguish different tastes transferred from the maternal diet."
The study looked at the healthy fetuses of 100 women between the ages of 18 and 40 years who were between 32 and 36 weeks pregnant in northeast England.
From this, 35 women were put into an experimental group that consumed an organic kale capsule, 35 were put into a group that took a carrot capsule, and 30 were put into a control group that was not exposed to either flavor.
Participants were asked not to consume any food or flavored 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 make sure it would not influence the results.
While carrot flavor can be described as "sweet" by adults, kale was chosen because it conveys more bitterness to infants than other green vegetables such as spinach, broccoli or asparagus, according to the study.
After a waiting period of 20 minutes post-consumption, the women underwent 4D ultrasound scans, which were compared to 2D images of the fetuses.
Lip corner pulling, suggestive of a smile or laughter, was significantly higher in the carrot group compared to the kale and control group. Whereas movements such as upper lip raises, the casting down of the lower lip, the pressing of the lips, and a combination of those -- suggestive of a crying face -- were much more common in the kale group than the other groups.
"By now, we all know the importance of (a) healthy diet for children. There are lots of healthy vegetables, unfortunately with (a) bitter taste, that is usually not appealing to children," said Ustun. She added that the study suggests "we might change their preferences to such foods before they were even born by manipulating" a mother's diet during pregnancy.
"We know that having a healthy diet during pregnancy is crucial for the health of children. And our evidence can be helpful to understand that adjusting maternal diet can promote healthy eating habits for children," she added.
Advances in technology have allowed for better images of the faces of fetuses in the womb, according to professor Nadja Reissland, head of the Fetal and Neonatal Research Lab at Durham University. Reissland, who supervised the research, developed the Fetal Observable Movement System (FMOS), with which the 4D ultrasound scans were coded.
"As technology gets more advanced the ultrasound imaging gets better and more precise," she told CNN, adding that this "allows us to code fetal facial movements frame by frame in detail and over time."
The researchers have now begun a follow-up study with the same babies post-birth to see if the flavors they experienced in the womb affect their acceptance of different foods during childhood, according to the press release.
All the women who participated in the study were White and British.
"Further research needs to be conducted with pregnant women coming from different cultural backgrounds," Ustun told CNN. "For example, I am coming from Turkey and in my culture, we love to eat bitter foods. It would be very interesting to see how Turkish babies would react to bitter taste."
She added that "genetic differences in terms of taste sensitivity (being a super taster or non-taster) might have an effect on fetal reactions to bitter and non-bitter tastes."