Most normal newborn’s head circumference is about 35 cm which is expected to grow to about 37 cm in the first month. A newborn’s brain is not fully developed and it has soft spots called fontanel. There are two such spots in your baby’s head. As these spots close at around 18-24 months the head circumference doesn’t grow much after that. Your baby’s head grows the fastest in the first four months after birth.
Sometimes there is extra fluid surrounding the brain this result in a large head circumference. Your pediatrician may ask you to do a CT scan to check for hydrocephalus (fluid surrounding the brain).
If the baby’s head circumference is smaller than average it may mean that your baby’s brain is not growing normally. This is called microcephaly (failure of brain development).
Head circumference also depends on the genes if the parents have a small head; your baby is likely to have a small head.