A new analysis has found that swaddling infants when they sleep on their stomachs or sides is linked to an increased risk of Sudden Infant Death Syndrome (SIDS).

The research, which focused on SIDS rather than swaddling, was carried out by a team from the University of Bristol who looked at four studies carried out over a period of 20 years.

"The focus of our review was not on studies about swaddling -- a traditional practice of wrapping infants to promote calming and sleep -- but on studies that looked at Sudden Infant Death Syndrome (SIDS)," said lead review author Dr Anna Pease, "We tried to gather evidence of whether there was an association between swaddling for sleep and SIDS."

The four studies also covered a diverse mix of populations and looked at participants in various parts of England, Tasmania in Australia, and Chicago in the United States.

The team found that the risk of SIDS when placing infants on the side or front for sleep increased when infants were swaddled, with the risk of SIDS almost double in infants who were swaddled and placed in the side position.

The studies also suggested that many of the infants found sleeping on their stomachs had moved into this position, and that the risks were also higher for older infants.

"We found some evidence in this review that as babies get older, they may be more likely to move into unsafe positions while swaddled during sleep, suggesting an age is needed after which swaddling for sleep should be discouraged. Most babies start being able to roll over at about 4 to 6 months,"  Dr Pease commented.

The analysis did have its limitations, with Dr Pease commenting that, "We only found four studies and they were quite different, and none gave a precise definition for swaddling, making it difficult to pool the results."

Despite these limitations, the results of the analysis not only support the current advice to avoid placing infants on their front or side to sleep, but also suggest that this advice may especially apply to infants who are swaddled.

  On a practical level, what parents should take away from this is that if they choose to swaddle their babies for sleep, always place them on their back, and think about when to stop swaddling for sleep as their babies get older and more able to move," Pease said.

The findings can be found in the journal Pediatrics.