Swaddling infants may increase their risk of sudden infant death syndrome (SIDS) during sleep, an analysis of previous research suggests.

Overall, babies wrapped in light cloth or blankets, a practice known as swaddling, were about 38 percent more likely to die of SIDS than infants who didn't get swaddled, researchers report in the journal Pediatrics.

"We know that safer sleep for babies means flat on the back," said lead study author Dr. Anna Pease of the University of Bristol in the U.K.

"The risk of SIDS when placing infants on the side or front to sleep increased when infants were swaddled," Pease added by email.

At least some of the SIDS risk tied to swaddling is due to babies getting older and able to roll onto their stomach or side even when parents correctly place them to sleep on their back, Pease noted. This typically happens between four and six months of age.

More on this...

At this point, "swaddling for sleep should be discouraged," Pease said.

SIDS has become much less common in recent decades as doctors have urged parents to put infants to sleep on their backs without pillows or other soft bedding and toys that could pose a suffocation risk. But it still remains a leading cause of infant mortality.

To assess how swaddling influences the risk of SIDS, Pease and colleagues pooled results from four studies done over two decades in the U.K., the U.S., and Australia.

Altogether, the studies included 760 babies who died of SIDS and 1,759 similar infants who didn't have SIDS.

In all four studies, the proportion of infants swaddled was higher in the SIDS cases than in the control cases. But the difference was only big enough to be meaningful in two of the studies.

Swaddled babies asleep on their stomachs had more than ten times the SIDS risk of unswaddled infants, the study found. On their side, swaddled infants had more than three times higher odds of SIDS, while the increased risk was 93 percent for babies on their back.

One limitation of the study is the wide variety of swaddling practices used in different regions of the world during different time periods, the authors note. Researchers also lacked data on whether infants slept in bed with their parents, which by itself can increase the risk of SIDS.

Even so, the findings should encourage parents to make sure babies sleep only on their backs, and if they're going to swaddle, to do so only when infants are too young to move out of that position during the night, said Dr. Danette Swanson Glassy of Mercer Island Pediatrics and the University of Washington.

"If you swaddle, be sure to end the practice long before the baby can roll to prone," Glassy, who wasn't involved in the study, said by email.

There's also a fine art to getting the swaddle just right to keep babies safe and comfortable, said Dr. Michael Goodstein, a researcher at Pennsylvania State University and director of the York County Cribs for Kids Program.

Overheating increases the risk for SIDS, so infants shouldn't be wearing heavy clothing before they're swaddled, Goodstein, who wasn't involved in the study, said by email.

"A swaddle should be firm, so the infant cannot get loose from it," because loose blankets in the sleep area are a risk factor for SIDS, Goodstein said. "But the swaddle should not be so tight as to restrict breathing, and it should allow for proper movement of the hips so as not to increase the risk of hip (injury)."

Other things that can lower the risk of SIDS include avoiding smoking in pregnancy or smoke exposure after birth and keeping the thermostat lower at night, said Helen Ball, a sleep researcher at the Durham University in the U.K. who wasn't involved in the study.

"Placing babies to sleep on their backs whether swaddled or unswaddled has been the most effective means of reducing SIDS deaths to date," Ball added.