Researchers in Toronto compared infants who received repeated heel lances during their first 24 to 36 hours of life to a control group of infants who didn't have to endure such frequent pain.
The lances were done to monitor the infants' blood sugar levels, since all were born to mothers with diabetes.
Blood was taken from the infants' heels every two to four hours. After 24 hours, a blood sample was taken from both groups of infants as part of a routine newborn screening test.
When that blood sample was taken, the babies who'd received the heel lances showed increased pain response in the form of crying and facial grimacing.
The babies actually showed pain behaviors before the blood sample was taken. They reacted as soon as the nurse wiped their hand with alcohol in preparation for collection of the blood sample.
Their response suggests they'd learned to anticipate pain, the researchers write in tomorrow's issue of the Journal of the American Medical Association.
"This was the first study to look at anticipatory pain responses in newborns. This research confirmed anecdotal reports that infants become hypersensitive to pain and learn to anticipate pain as a result of cumulative exposures to pain," says lead author Dr. Anna Taddio, an assistant professor of pharmacy at the University of Toronto and an associate scientist and pharmacist at the Hospital for Sick Children.
"Many newborn infants undergo painful, invasive procedures after delivery for medical reasons, and it is important for us to understand how they react to pain, and look at ways to decrease their pain," Taddio adds.
For more on child development, try Tufts University.