But can it work in babies born as early as 28 weeks' gestation? The answer is a qualified yes, Johnston and colleagues now find.
These "very preterm" babies do seem to feel a bit less pain when cuddled by their mothers while nurses obtain blood samples from a heelstick. Even more importantly, the babies recover from the painful experience much faster when cuddled.
"The pain response in very preterm neonates appears to be reduced by skin-to-skin maternal contact," Johnston says in a news release. "This response [to cuddling] is not as powerful as it is in older preterm babies, but the shorter recovery time using kangaroo mother care is important in helping maintain the baby's health."
Kangaroo mother care was invented in 1978 by Colombian pediatrician Edgar Rey. Faced with a shortage of incubators, Rey found that mothers could use their own bodies to warm premature infants. Years of study show the technique to be at least as safe and effective as incubators, and it lessens mothers' anxiety while promoting mother/infant bonding and breastfeeding.
The technique calls for the tiny child to be held upright between the mothers' breasts and covered with a blanket. Because the child must be held upright against warm skin 24 hours a day, mothers can share kangaroo care with fathers and others.
The Johnston study enrolled babies who needed at least two blood draws via heelstick. They performed one heelstick while the baby lay in an incubator, and another while the baby was being held in kangaroo care. The babies' facial expressions were videotaped, and researchers monitored their vital signs.
It's hard to judge exactly how much pain a premature infant is feeling. The researchers used a scale called the premature infant pain profile, a composite measure of physiological and behavioral signs.