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Full-term fetus knows mom's voice: study

By Alison McCook

Last Updated: 2003-05-27 9:54:26 -0400 (Reuters Health)

NEW YORK (Reuters Health) - New study findings suggest that shortly before birth, a fetus may be able to distinguish mom's voice from others.

U.S. researchers found that heart rate in full-term fetuses increased when a recording of their mothers' voices was played, but decreased in response to the voice of a female stranger.

This shows that the fetus can distinguish between the voices of its mother and other women before it is even born, study author Dr. Barbara S. Kisilevsky of Queen's University in Canada told Reuters Health.

"It is not the increased heart rate per se, but the different ways in which the fetuses responded to the two voices ... that tells us that the fetus had to recognize its own mother's voice," she said. "If not, then the response to both voices would have been the same."

These results add to a body of research suggesting that biology prepares the fetus to bond to its mother after birth and take on the daunting task of learning language, Kisilevsky noted.

Furthermore, showing that a fetus can distinguish its mother's voice adds credence to the theory that both genes and experience help a fetus understand speech, because the tendency to respond differently to different voices "had to occur through experience," Kisilevsky said.

During the study, reported in the May issue of the journal Psychological Science, Kisilevsky and her colleagues played a tape recording through speakers held around 10 centimeters over the mothers' abdomens.

The tapes consisted of two minutes of silence followed by two minutes of either the mother or a female stranger reading the same poem, then two more minutes of silence.

On average, the fetuses had spent about 38 weeks in the womb, and so were full-term. Thirty fetuses were exposed to tapes of their mothers speaking, and another 30 the voices of a female stranger.

Although mothers' voices did not appear to elicit significantly more body movement in the fetuses than did the voices of female strangers, fetal heart rate increased when listening to their mothers, and appeared to decrease in response to a recording of a female stranger.

In terms of why a stranger's voice might lower a fetus's heart rate, Kisilevsky said that a decrease in heart rate is often a sign of attention, and the fetus may have paid more attention to a voice it didn't recognize.

"I think it already knew its mother's voice, and was now learning about other voices," she said.

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