A: Swaddling has many benefits for your baby, but it is true that incorrect swaddling may cause hip dysplasia, a common cause of hip arthritis in young people. (The term hip dysplasia can describe anything from a shallow hip socket all the way to a completely dislocated hip.) Tight, prolonged swaddling with the legs straight interferes with proper hip development and can even cause immature hips to dislocate. This should be avoided by using swaddling techniques that allow plenty of room for the hips to move freely and for the legs to bend and move, so the baby’s hips can develop naturally. Swaddling the arms doesn’t cause any harmful effects, but tight swaddling of the legs should be avoided.
Human babies are born in an immature condition compared to most other creatures. For example, a newborn deer can stand within 10 minutes and walk within seven hours because their hips are well-developed at the time of birth.
In contrast, human hips are shallow and have somewhat flexible sockets at the time of birth. The birthing process causes one in six babies to have some hip instability, and approximately one or two per 1,000 babies will have a dislocated hip at the time of birth. Pediatricians will always examine the infant’s hips shortly after birth because hip instability is the most common abnormality in newborn babies. Fortunately, the hip ligaments can tighten up and become normal as long as the natural infant position is encouraged for a few weeks.
The natural infant position is where the hips are bent up and the thighs spread like a child squatting, so it’s best to avoid attempts to straighten the knees and hips while swaddling. With time, the hip sockets will become stronger, and the baby will gradually stretch out her own hips. This generally takes two to three months, but tight leg swaddling should be avoided for the first six months of life just to be on the safe side.
There are many swaddling techniques and commercial swaddling blankets are available to make the process easier. It’s best to avoid those that wrap the legs and especially avoid the ones that wrap the legs in a straight position.
—Charles T. Price, MD, FAAP, director of the International Hip Dysplasia Institute