Researchers at the University of Helsinki in Finland found that babies were able to recognize words played for them in the womb.
The better we know how the fetus’ brain works, the more we’ll know [about] early development of language. —Eino Partanen

Some mothers may be careful about what they say around their children, but new research suggests that a mother's unborn child is listening, too.

The study, published in the Proceedings of the National Academy of Sciences, reinforces what many people believed — babies hear what is said to them in the womb and their brains recognize these words after birth.

Researchers at the University of Helsinki in Finland examined 33 mothers during their third trimester of pregnancy. Out of the 33 participants, 17 listened to a CD that loudly played two, four-minute sequences of the made-up words "tatata" or "tatota," pronounced differently with varying pitches from week 29 to birth.

The words were repeated 50 to 71 times. Following birth, all 33 babies were tested for normal hearing and then were scanned with an EEG (electroencephalograph) to see if the newborns reacted differently to the same made-up words they were exposed to in the womb.

Researchers found the babies who listened to the CD recognized the words and were able to distinguish between the pitch changes due to increased brain activity. The babies who did not hear the CD in utero did not have increased brain activity, thus were not able to recognize the words or distinguish pitch changes.

"We presented variants of words to fetuses; unlike infants with no exposure to these stimuli, the exposed fetuses showed enhanced brain activity (mismatch responses) in response to pitch changes for the trained variants after birth. Furthermore, a significant correlation existed between the amount of prenatal exposure and brain activity, with greater activity being associated with a higher amount of prenatal speech exposure," the study said.

Eino Partanen, a doctoral student and lead author on the paper, told NBC News the research adds to what has previously been discovered.

"We have known that fetuses can learn certain sounds from their environment during pregnancy," Partanen said. "We can now very easily assess the effects of fetal learning on a very detailed level — like in our study, [we] look at the learning effects to very small changes in the middle of a word."

Minna Huotilainen, who also worked on the study, published research in 2005 that showed fetuses could discriminate between sounds. In 1988, a study published in the British medical journal Lancet that showed babies were able to recognize the theme song melodies and melodic cues into the soap operas their mothers watched during pregnancy.

According Partanen, mothers should not suddenly subject their fetuses to loudspeakers just because they can learn in the womb. Partanen said there is no solid evidence that stimulation beyond normal sounds of everyday life offers any long-term benefits to healthy babies. Developmental psychologist Christine Moon, of Pacific Lutheran University, added that overstimulation of audio to the fetus could interfere with the unborn child's brain development, auditory system, fetal ear and sleep cycles.

Partanen believes that the findings can be beneficial for future studies on how to help babies at risk for dyslexia or auditory processing disorders, or who are not necessarily going to be healthy when they are born.

“The better we know how the fetus’ brain works, the more we’ll know [about] early development of language,” Partanen told Science magazine. “If we know better how language develops very early, we may one day be able to develop very early interventions [for babies with abnormal development].”