As technology advances so does our ability to monitor unborn babies. Now it’s even possible to track how a very young fetus, still in its mother’s womb, learns and remembers basic speech.
As a labour and delivery nurse in the 1980s, the limits and potential value of monitoring a fetus always intrigued me. The research of Anthony DeCasper a decade later really caught my interest – demonstrating early learning and memory capabilities.
In a recent piece of research, my team and I decided to use a fetal monitor similar to those used in traditional labour and delivery units to record a fetus’s heart rate in response to a recording of a passage of speech. We did this to help us understand more about how early a fetus could learn a passage of speech and, if learned, whether the passage could be remembered as long as four weeks later.
Because the fetus cannot speak to us, we used a small change in heart rate called the “cardiac orienting response” to determine when and for how long the fetus could remember. The conventional interpretation of this kind of response is that it shows the heart-rate decelerating because of a stimulus. Researchers have used this response for decades in newborns and some hypothesise that it indicates familiarity with a stimulus or learning.
In our study, from 28 to 34 weeks of pregnancy, mothers spoke a passage or nursery rhyme out loud twice a day and then came in for testing at 28, 32, 33, and 34 weeks gestational age. The nursery rhyme was untitled and it was therefore unlikely for mothers to have heard it before.
During testing, we decided to make things a bit more difficult for the fetus. Rather than play back a recording of the mother speaking the rhyme, instead, we played a recording of a female stranger speaking the same rhyme. We believed this would help us determine whether the fetus was responding simply to its mother’s voice or to a familiar pattern of speech – a more difficult task.
At 34 weeks gestational age, we asked mothers to stop speaking the passage out loud so that we could then see how long the fetus could remember the pattern of speech.
Interestingly, the fetus’ heart rate began to respond by 34 weeks gestational age – or once the mother had spoken the rhyme out loud for six weeks. The fetuses in this study continued to respond in the same way for as long as four more weeks after the mother had stopped saying the rhyme, or until 38 weeks gestational age – just before birth.
This should not be entirely surprising, because a mother’s voice is a predominant source of sensory stimulation for her developing fetus and, while speaking, not only does her fetus hear but, it also feels her vertebral column and diaphragm gently vibrate and move in sync with her speech.
So our findings should not be used to suggest alterations in the typical ways mothers interact with their unborn baby. But they do highlight just how sophisticated the third trimester fetus really is and suggest that a mother’s voice can be involved in the development of early learning and memory capabilities.