April 30 (HealthDay News) -- Results of a small study show that the electromagnetic field produced by incubators affect the heart rates of newborn babies, Italian researchers report.

Whether these changes in cardiac rhythms have long-term effects isn't known, but they could have implications for premature infants who can spend several weeks or months in incubators, the researchers said.

"Neonatal incubators are designed to shield fragile babies from external foes and to preserve their temperature, and they are good for this. Yet we showed that most of them produce relevant electromagnetic fields, and this study is the first to show that this exposure has an influence on babies' autonomous nervous system," said lead researcher Dr. Carlo Bellieni, of the University of Siena's Department of Pediatrics, Obstetrics, and Reproductive Medicine.

"Neonatal incubators are not electromagnetically neutral, and this data deserves as much attention as the concerns about risks from cellular phones or high voltage lines on adults," he said.

However, Bellieni doesn't think that people should be overly concerned by this phenomenon.

"Alarm is not justified, because incubators are necessary to babies and because no long-term effect of this exposure has been demonstrated on babies' health," Bellieni said. "Thorough analyses of possible long-term effects of this exposure are needed."

The report was published in the May issue of the Archives of Disease in Childhood.

In the study, Bellieni's team looked at the changes of heart rates among 43 newborns, who were critically ill or premature. The researchers assessed the heart rates of 27 babies over three five-minute periods during which the incubators motor was left on, then switched off and then turned on again.

To determine if the noise of the motor might be a factor, 16 of the infants were exposed to background noise, while the incubators motor was turned off.

Bellieni's group found that background noise did not affect heart rate. However, heart rate was significantly affected by the incubators. When the incubator was turned on, the heart rate variability dropped significantly, the researchers found.

A drop in heart rate variability is a strong predictor of poor outcomes in adult patients with heart disease, the researchers noted.

SOURCES: Carlo Bellieni, M.D., Department of Pediatrics, Obstetrics, and Reproductive Medicine, University of Siena, Siena, Italy; May 2008, Archives of Disease in Childhood