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Swaddling a baby may increase the risk for sudden infant death syndrome, or SIDS, a new analysis concludes.

The practice of swaddling — wrapping an infant with a light cloth, with the head exposed — has grown in the United States with reports that it promotes better sleep.

Researchers pooled data from four observational studies of SIDS and swaddling that included 760 SIDS cases and 1,759 controls.

Over all, swaddling increased the risk for SIDS by about one-third. The risk was greatest in babies sleeping on their stomachs, less in those sleeping on their sides, and least in infants sleeping on their backs. The study is in Pediatrics.

The lead author, Anna S. Pease, a research associate at the University of Bristol in England, said that the results should be interpreted with caution, because there are few studies of the subject, and the amount of good evidence is limited.

Still, she said, “We already know that side and prone sleeping are unsafe for young babies, so the advice to place children on their backs for sleep is even more important when parents choose to swaddle them.”

The risk also increased with the age of the infant.

“We suggest that parents think about what age they should stop swaddling,” Dr. Pease said. “Babies start to roll over between four and six months, and that point may be the best time to stop.”