Pediatricians measure an infant's head growth, or head circumference, along with height and weight on a regular basis to determine if the rate is age and gender appropriate. Although head circumference varies with each infant, pediatricians look for a trend in head growth from month to month. Growth charts can help determine if head growth is on track or if there is a cause for concern.
Measuring Head Circumference
Pediatricians measure head circumference by placing a tape measure around the largest part of the infant's head. The tape measure is typically placed above the eyebrows and ears and extended around the back of the infant's head, according to the website Medline Plus. A pediatrician usually takes this measurement at each of the baby's checkups.
Infant Growth Charts
The Centers for Disease Control provides growth charts for infants, children and adolescents. Pediatricians use them to help determine if growth seems to be on track. The CDC has head circumference growth charts on its website.
How to Read Growth Charts
There are separate head circumference growth charts for infant and toddler boys and girls. Percentiles on each chart range from the 5th to 95th percentile. If a baby's circumference is around the 50th percentile, about half of the babies his age have larger heads, and about half have smaller heads. Most pediatricians will look for a steady trend, meaning that from month to month a child's head remains in approximately the same percentile. Pediatricians typically become concerned when head growth seems to slow or if the circumference is extremely small or large based on the growth charts.
Microcephaly is a condition in which a baby has a smaller than normal head that fails to grow during infancy. Microcephaly occurs when an infant's brain has not developed properly or has stopped growing, according to the National Institute of Neurological Disorders and Stroke. An infant may also experience delayed development or mental retardation, or he may have normal intelligence but a small head. Microcephaly can be caused by genetic abnormalities or mothers who have abused drugs or alcohol during pregnancy or have been been exposed to certain diseases or toxic chemicals.
Craniosynostosis, a condition in which a baby's soft spot closes before the brain develops completely, can also cause a smaller than normal head size according to the Mayo Foundation for Medical Education and Research. Craniosynostosis typically requires skull surgery to make room for the brain to grow.
Macrocephaly is a medical condition in which an infant's head circumference is larger than normal. Unlike microcephaly, infants with macrocephaly may have a large brain and are more likely to have normal mental development, according to the National Institute of Neurological Disorders and Stroke. But some forms of macrocephaly are associated with mental retardation.