The long-held practice of swaddling, or tightly wrapping in a blanket, our infant children in order to soothe their spirits may also increase their risk of sudden infant death syndrome (SIDS), finds a new review published Monday in Pediatrics.

The researchers analyzed the combined data from 4 earlier studies, ultimately examining 760 cases of SIDS among 2,519 children. After adjusting for age and other variables, they found that swaddled children were about one-third more likely to die of SIDS than their non-swaddled counterparts. Though the risk was highest in swaddled children who slept on their stomach and sides, even swaddled children who slept on their back were more likely to die of SIDS than non-swaddled children who slept on their back.

“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,” lead author Dr. Anna S. Pease, a research associate at the University of Bristol in England, told The New York Times.

Swaddled children who were older than six months also had a higher risk of SIDS, possibly because these children had a “greater likelihood of rolling” onto their stomachs or side while sleeping than did younger infants, the authors wrote.

Alarming as these findings are, Pease and her colleagues are quick to note they aren’t declaring a fully conclusive link. The studies reviewed were relatively small, had varying definitions of swaddling, and they found it difficult to exclude the possibility of other unknown factors that might better account for the connection. Similarly, because all the data they examined was observational, it's impossible to say whether swaddling has a direct cause-and-effect relationship to SIDS from this study alone.

They do however have some practical recommendations for any concerned parents.

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

According to the Centers for Disease Control and Prevention, there are around 3,500 sudden unexpected infant deaths in the U.S. annually, with 44 percent of these cases, or 1,500, fitting the criteria for SIDS. It remains the leading cause of death in infants between the ages of 1 to 12 months.

Source: Pease A, Fleming P, Hauck F, et al. Swaddling and the Risk of Sudden Infant Death Syndrome: A Meta-analysis. Pediatrics. 2016.