In order to find the ideal way to carry a baby we have to take a look at baby’s anatomy. When a baby is born, some of his skeleton is still cartilage and not yet proper bone. Ossification (= cartilage becoming bone) is a process that takes years and is finished when a human being is fully grown up.
One part of baby’s body that contains a lot of cartilage is the pelvis. It initially consists of several bones that are held together by cartilage. In a newborn, where the femoral head (top of the upper leg bone) meets the hip socket (acetabulum), three bony parts of the pelvis are joined together by cartilage and everything is still a bit soft. Also the femoral head is still formed by cartilage. Ossification of the pelvis and the femoral head happen gradually and are usually finished within the first 9 months of life. Especially in this time it’s important to aid the development of the hip by supporting correct positioning of the femoral head because wrong positioning, such as tight swaddling, may lead to hip dysplasia.
There is an ideal leg position which centres the femur head right in the middle of the hip socket and thus aids the development of baby’s hips. It’s described as M-position, frog-position or spread-squat-position and means that baby’s knees are higher up than his bottom and that his legs are spread apart ca. 90° (for those with medical background: legs should be flexed min. 100°, abduction should be 30-45°). Babies automatically assume this position when lifted up, because it’s also ideal for being carried on the mothers hip. Also babies treated for hip dysplasia using a Pavlik harness or Frejka pillow have their legs in this position.
A baby carried in the M-position will have a rounded back because the tilt in the pelvis causes the spine to become rounded and viceversa. In a cradle carry (baby is lying on her back in a hammock-style sling) a correct M-position cannot be achieved because her legs cannot be spread. So this position is not recommended at all by hip dysplasia specialists. Instead upright positions, especially on the mothers hip are better for the hip, if a carrier supports correct positioning and a round back.
A good carrier allows the baby to be carried in the M-position. This is not possible if the fabric in baby’s crotch is too narrow (it should support the whole upper leg and reach from knee to knee) or if baby’s legs are spread too far apart. So before buying a baby carrier check how a baby sits in there, either by trying it out with your baby or by looking at photos.
Imagine what it would feel like for you to sit in a baby carrier: Wouldn’t you prefer to have your whole upper legs supported instead of dangling from your crotch?