The average circumference of a newborn's head is between 34 and 35 centimeters, according to The American Academy of Pediatrics. A newborn's head grows as much as 3 centimeters in circumference by one month. Pediatricians monitor the growth of the baby's head to ensure proper brain development.
A baby's skull isn't fully formed at birth as the brain is still developing, notes The American Academy of Pediatrics. A newborn's head continues to form and grow exponentially in the first four months after birth. A vaginal delivery may cause the baby to form an irregular cone-head shape at the time of delivery, but this should correct itself in the first week, explains HealthLinkBC.