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.
"The wrap should be tight at the top and looser at the bottom." Tight swaddling around the hips and legs could lead to delayed walking among children born with a hip abnormality, says Dr Hiscock of the Murdoch Children's Research Institute.
It can also lead to hip-replacement surgery when the children reach middle age.
Prof Clarke's article says the one in five babies born with a hip abnormality areat most risk from traditional swaddling.
The article raises concerns about renewed popularity of full-body swaddling in the English-speaking world.
It says 90 per cent of US infants are swaddled in the first six months and the practice is increasing in other countries.
It points to 2012 Australian research that highlights a three-fold increase in developmental hip dysplasia at one hospital.
The article says a Japanese program to encourage grandmothers not to swaddle their grandchildren led to a 50 per cent drop in the prevalence of hip dislocation.
It says early diagnosis leads to relatively simple and successful treatment of the condition, but highlights controversy over whether babies should be screened for the condition.
The article says it is essential that health professionals provide the correct advice about safe swaddling.