A: Both swaddling and babywearing have social and emotional benefits for infants and parents. However, prolonged positioning with the legs in a straightened position increases the risk of poor hip development and could even cause dislocation. Hip instability is the most common abnormality in newborn infants, occurring as often as one in six infants.
Fortunately, hip instability improves automatically in 90 percent of babies as long as the hips are allowed to mature naturally. However, hip dysplasia (poor hip growth) is the most common cause of hip arthritis in young women and leads to approximately 10 percent of all total hip replacements in the USA. It is more common when other family members have hip dysplasia, in firstborn girls, babies in the breech position (bottom down instead of head first), or when babies’ legs have been tightly swaddled.
The time to influence hip development is during the first six months of life because this is a period of rapid growth. This is best accomplished by allowing the hips and knees to bend and spread naturally. Swaddling the upper body is enough to calm most babies, so the legs should have room to move freely and assume positions with the knees and hips bent. When carrying young infants, it’s best if they face the mother with the thighs fully supported and in the M-position (where the buttocks is lower than the knees). After 6 months of age, the hips have developed enough that position rarely matters.
—Charles T. Price, MD, FAAP, director of the International Hip Dysplasia Institute