Prince George, the son of Britain's Prince William and his wife Catherine, was swaddled as a newborn. CARL COURTCARL COURT/AFP/Getty Images
Prince George, the son of Britain's Prince William and his wife Catherine, was swaddled as a newborn. CARL COURTCARL COURT/AFP/Getty Images

After seeing a recently posted photo of Kim Kardashian’s perfectly swaddled baby, I wondered how she got the blanket wrapped so tightly around her four-month old. All three of my kids were swaddled as newborns in the hospital—as are 90 percent of babies in the United States. The cocoon-like wrapping purportedly keeps babies from jerking themselves awake when they thrash out their arms and legs in a startle reflex.

But my husband and I could never master the wrap at home. Our babies would kick the blanket away and quickly come unbound.

As it turns out, that may have been a good thing. A provocative review of recent studies published this week in the British journal Archives of Disease in Childhood found that while swaddling does help infants sleep better at night and might help soothe colic symptoms—another of its purported benefits—it could raise the risk of serious hip problems later in life that necessitate hip replacements by middle age.

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That’s because infants are usually swaddled with their legs extended straight; if the blankets are wrapped too tightly for babies to bend their legs, their hips could receive too much pressure over time, causing an abnormal formation of the hip socket called dysplasia. If it persists into adulthood, the condition can cause painful inflammation and arthritis sometimes leading to hip replacements before age 40.

Australian researchers measured a 300 percent increase in hip dysplasia in babies at one hospital, which they attributed to a recent rise in swaddling. Japanese researchers saw a drop in hip problems after grandmothers were taught to abandon the practice on their grandchildren.

Because swaddling can have soothing benefits—and promote nerve and muscle development in preterm infants—it doesn’t necessarily have to be avoided altogether. But parents should take precautions to make sure it’s done safely.

“The babies’ legs should not be tightly wrapped in extension and pressed together,” wrote the article author Dr. Nicholas Clarke, an orthopedic surgeon at the University Hospital Southampton, Great Britain. “Commercial products for swaddling should have a loose pouch or sack for the babies’ legs and feet, allowing [for] plenty of hip movement.”