Celeste Johnston of McGill University in Montreal and colleagues had previously shown that skin-to-skin contact, known as kangaroo mother care, helps babies born at 32 to 36 weeks to recover from pain.

It was believed babies born between 28 and 31 weeks were not developed enough to benefit from comfort strategies.

The researchers conducted a randomized crossover trial to see whether young babies could bounce back from pain following a heel lance blood test -- pricking the baby's heel to obtain a blood sample.

The team asked mothers to hold their babies for 15 minutes prior to and throughout a heel lance procedure and on the another occasion the same babies were treated as normal. The team assessed the babies' pain based on facial expressions, heart rate and blood oxygen levels.

The study, published in the journal BMC Pediatrics, babies receiving kangaroo mother care recovered from the pain within a couple of minutes, whereas the incubator babies were still suffering at more than three minutes.

This delay could make all the difference to the health of a very preterm baby, the researchers said.