Parents who swaddle their baby should ensure the hips and legs have free movement, according to an expert worried about the increased popularity of the traditional full-body wrap.
The main concern is the hips, says UK Professor Nicholas Clarke.
Many babies sleep better when swaddled but this can be achieved by focusing on the top half of the body, he writes in the Archives of Disease in Childhood published by the British Medical Journal.
Australian paediatrician Dr Harriet Hiscock agrees.
"Parents who are going to wrap need to learn to do it in a safe way. The baby must be able to fully stretch out their legs.