Fetuses learn not to be surprised -- and researchers learn from them


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Fetuses can remember, potentially long enough to shed light on their neural development.

Dutch researchers have found that, at 30 weeks of development, fetuses have a memory of 10 minutes. At 34 weeks old, they can remember events for four weeks. The findings help explain central nervous system development -- and how fetuses may react if that growth is abnormal.

In the study, researchers in the Netherlands applied a sound-and-vibration stimulus to the abdomens of 93 pregnant women. The stimulus lasted for one second and was repeated every 30 seconds, at a location just above the fetus’ leg. The fetuses ranged from 30 weeks to 38 weeks.


At first, the fetus would make a startled-like movement, says study coauthor Dr. Jan Nijhuis, director of the Centre for Genetics, Reproduction and Child Health at Maastricht University Medical Centre in the Netherlands. Eventually though, it would stop reacting. The researchers then counted the number of stimuli before the fetus stopped responding.

“The fetus needs to know which sounds are stressful and which are safe. Otherwise, it would be completely distressed all day long because it hears noises of the maternal gut and heart,” Nijhuis says.

Ten minutes after the fetuses had adjusted, they received the same stimuli again. Fetuses as young as 30 weeks stopped responding to these stimuli sooner than they had the previous time, demonstrating a short-term memory of 10 minutes.

To look at longer term memory, researchers repeated the experiment when fetuses were 38 weeks old. Fetuses who had been 34 weeks old at the time of the initial experiment adjusted significantly faster when they were 38 weeks old, suggesting that they could store and retrieve information four weeks later. These fetuses also adjusted more quickly than those that were 38 weeks old and had not been previously exposed to the stimuli.

That adjustment process is called habituation, and it requires an intact central nervous system. Previous studies have shown that fetuses with lags in behavioral development or Down syndrome take longer to habituate.

“Habituation is a form of learning,” Nijhuis says. “If you live near the train station, you learn to tune it out and sleep through it. But other noise would wake you up, even if it were small. Habituation is a memory for safe noises.”


The findings shed light on central nervous system development, and Nijhuis says the ultimate goal is to distinguish a normal fetus from one at risk of developmental problems. Such an assessment could affect the timing of the delivery.

“We want to look at the fetus and understand it better,” Nijhuis says. “We want to ask: is the baby better in [the womb] or better out?”

The findings were published in the July/August issue of Child Development.

-- Shara Yurkiewicz