It's all very scientific.
You, like me before, may say to yourself, if you're right-handed then obviously you'll carry with your left arm... BUT wait! It's not about that. In fact, the reason goes back centuries...
In fact, 70-85% of the world’s population prefers the left-arm baby carry to the right one. A new Nature Ecology and Evolution study suggests women carry their babies on their left side because they are wired to do so—whether or not they are right-hand dominant.
According to the study, “the preference to hold infants on the left rather than the right side of the body, as reported in human populations, reflects socio-emotional processes and potentially facilitates mother-infant relationships.”
If your baby is on the left side, that reportedly means that your right brain is in tune with the baby’s emotional cues. Doesn't get more maternal than that!