Babies in the womb smile over carrots, grimace at kale, new fetus study finds

Images from fetuses in the womb show they smiled after their mothers ate carrots but scowled over kale, a new study released this week shows.

"Findings of this study have important implications for understanding the earliest evidence for fetal abilities to sense and discriminate different flavors," researchers wrote in study findings released Wednesday.

According to the recent study of 99 pregnant women and their fetuses in England, researchers gave the mom's capsules containing powdered versions of the two foods.

Some previous studies have proposed that infants can begin a "social smile" about two months after birth. The authors of this study said its implications could further our "understanding of the development of human oral and nasal chemoreception, including the nature and timing of behavioral reactions to prenatal flavor exposure," not about an infant's ability to signal positive emotions.

The study, published in a journal titled Psychological Science, consisted of white British women between the ages of 18 and 40.

Thirty-five of them ingested a one medium-sized carrot, and 34 women consumed the equivalent of 100 grams of chopped kale. The remaining mothers didn't ingest either food.

Twenty minutes later, researchers said, 4D ultrasound scans showed most of the fetuses exposed to kale appeared to grimace, while most exposed to the carrot appeared to be laugh. The control group, meanwhile, did not have the same responses.

"We show the first direct evidence that fetuses react to the flavors of the foods eaten by their mothers," Beyza Ustun, a co-author of the study and the head of the Fetal and Neonatal Research Lab at Durham University, tweeted Thursday.

Best way to get a crying baby to sleep?:Researchers say they've figured it out

Pregnancy stress level study:Stress levels during pregnancy linked to 3-month-old babies who cry, fuss more, study finds

"When fetuses were exposed to carrot flavor, they were more likely to show 'laughter-face' reactions, and when they were exposed to kale flavor, they were more likely to show 'cry-face” reactions'," researchers wrote. "We also found that facial responses to flavors became more complex as fetuses matured."

Some previous studies have proposed that infants can begin a "social smile" about two months after birth. 

The authors of this study said its implications could further our "understanding of the development of human oral and nasal chemoreception, including the nature and timing of behavioral reactions to prenatal flavor exposure."

The fetuses in the new research were at 32 to 36 weeks’ gestation, researchers said. An average pregnancy lasts 40 weeks from the last menstrual period.

Exclusive: USA TODAY's coverage of maternity health 'deserts'

• Maternal health:Maternal mortality rates are higher for rural women of color. Data, charts, and maps show the disparity.
• Maternal health:In rural America, maternal health care is vanishing. These moms are most at risk.
• Maternal health:Inequities in maternal health care access are not new. They have deep roots in history.
• Maternal health:Native Americans given promise of health care. For rural moms, it's an empty one.

Natalie Neysa Alund covers trending news for USA TODAY. Reach her at nalund@usatoday.com and follow her on Twitter @nataliealund.