Babies undergoing a painful medical procedure show less pain when they're in mom's arms instead of dad's, a new study shows.

Reuters Health reports that researchers observed 62 premature babies in neonatal intensive care as they had blood drawn from their heels for tests.  The mothers and fathers alternated holding their babies for each blood test. Researchers videotaped the babies' faces, and then analyzed the tape for signs of pain, "such as squeezed eyes and a furrowed nose and lip," Reuters said.

Babies exhibited fewer pain signs when their mothers held them. Researchers suspect the difference could be related to anatomy. "The difference in the male physique, especially the chest, may be perceived by the infant to be not that of a natural caregiver," the scientists said.

Still, the difference between mom and dad was small, and the study may be more important for showing the benefits for preemies of skin-to-skin contact with their parents. Also called "kangaroo care," this involves nestling an undressed baby against the parent's bare skin, and then covering the parent and baby with a blanket.

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