Previous studies have shown babies during their last weeks in the womb could recognize their mother's voice and vocal melody but the researchers say their new study suggests they've learned much more than that.
"We showed that the fetus during the last 10 weeks of the pregnancy not only listens to but remembers and learns languages," Patricia Kuhl at the University of Washington Institute for Learning and Brain Sciences told the BBC.
The researchers studied 40 infants in Sweden and the United States who were just 30 hours old, having them listen to vocal sounds in Swedish and English.
The U.S. babies would start sucking their pacifiers more intently when they heard Swedish vowels, while Swedish babies reacted similarly when they heard English sounds, an effect the researchers said suggested they reacted differently to their native tongue and a foreign language and could, in effect, hear the difference.
The findings suggest the brain of an infant in the womb has more advanced capabilities than previously believed, the researchers said.
"The brain goes online like a curious and capable learning mechanism," Kuhl said. "If you release that curiosity anything can happen."