According to medical researchers fetuses can remember, potentially long enough to shed light on their neural development.

They have a memory of 10 minutes and at 34 weeks old they can remember events for four weeks. "In addition, results indicated that 34-week-old fetuses are able to store information and retrieve it four weeks later," said the researchers.

The study was conducted by scientists from the Department of Obstetrics and Gynecology at Maastricht University Medical Centre and the University Medical Centre St. Radboud, both in the Netherlands.

The researchers applied a sound-and-vibration stimulus with a "fetal vibroacoustic stimulator," a hand-held diagnostic device used to gauge an unborn baby's heart rate and general well-being to the abdomens of 93 pregnant women.

The fetuses ranged from 30 weeks to 38 weeks and the stimulus lasted for one second and was repeated every 30 seconds, at a location just above the fetus' leg. This was repeated on five occasions during the last eight weeks of their pregnancies.

The baby's responses essentially eye, mouth and body movements were closely monitored over the weeks with ultrasound imaging to gauge "fetal learning" patterns.

Study coauthor Dr. Jan Nijhuis, director of the Centre for Genetics, Reproduction and Child Health at Maastricht University Medical Centre in the Netherlands said at first the fetus would make a startled-like movement.

The researchers noted that "The stimulus is then accepted as 'safe'" by the babies, and once the babies got accustomed to the sound they stopped reacting, a process known as "habituation."

"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 said.

The researchers counted the number of stimuli before the fetus stopped responding. 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.

The fetuses were found to improve these skills as they grew older, with those who were 34- or 36-weeks old clearly showing that they had become familiar with the hum outside the womb.

Researchers repeated the experiment when fetuses were 38 weeks old, to examine long term memory and reported that 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.

"The fetus 'remembers' the stimulus and the number of stimuli needed for the fetus to habituate is then much smaller," the study said.

The researchers said the findings could help obstetricians track the healthy development of unborn babies during pregnancy. This is as the adjustment process called habituation, 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 highlight the central nervous system development, and Nijhuis said the ultimate goal is to distinguish a normal fetus from one at risk of developmental problems.

"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 research was published in Child Development, a medical journal.