About a third of the women were given capsules containing powdered versions of one of the vegetables; about a third given capsules of the other; and about a third given neither.
Ultrasound tests 20 minutes later showed most of the babies exposed to kale seemed to grimace, and most given carrots appeared to laugh, said the report published by Psychological Science. The control group did not have the same responses.
"We are the first ones who could actually show on an ultrasound scan the facial expressions in relation to the food which the mother has just consumed," Nadja Reissland, a co-author of the study and the head of the Fetal and Neonatal Research Lab at Durham University, told NBC News.
The babies in the research were at 32 to 36 weeks’ gestation. Pregnancy usually takes 40 weeks from a woman’s last period.
The reactions of these babies were similar to faces kids or adults make when tasting something bitter, Reissland said. But it is unknown if babies in the womb experience emotions or dislikes in a similar way. And the grimaces could just be muscle movements reacting to kale’s bitter taste, she said.
The study could help show how eating habits might be shaped by exposure to flavors in the womb, she said.
Mothers who eat healthy diets while pregnant may have babies who are less fussy eaters, Reissland said.