The head circumference (HC) measurement is a standard procedure performed shortly after a baby is born. This metric, also known as the Occipitofrontal Circumference (OFC), measures the distance around the largest part of the baby’s head, typically from the forehead to the back of the skull. It serves as a foundational assessment tool for a newborn’s overall health and developmental status, providing a baseline for tracking growth over time.
Defining the Average Measurement
For a full-term newborn, the average head circumference generally falls within a narrow range, typically 34 to 35 centimeters (cm) or about 13.5 to 14 inches. Boys tend to have a slightly larger average head circumference than girls, though the difference is usually less than 1 cm. These figures represent the 50th percentile. A measurement that falls between the 5th and 95th percentiles is considered within the expected range for a healthy newborn.
The Importance of This Newborn Screening
Healthcare providers take this measurement because head size offers a direct, quantifiable estimate of brain volume and growth. The brain undergoes its most rapid growth phase during infancy, and the skull must expand to accommodate this development. Therefore, measuring the Occipitofrontal Circumference is a proxy for assessing neurological development. The initial reading is plotted on specialized growth charts, such as those from the World Health Organization (WHO) or the Centers for Disease Control and Prevention (CDC), which are adjusted for age and sex.
Tracking the head circumference on these charts allows clinicians to monitor the pattern of growth over time, which is more informative than any single measurement. A consistent growth trajectory is a positive indicator that the central nervous system is developing as expected.
What Measurements Outside the Norm Indicate
When a newborn’s head circumference falls significantly outside the average percentile range, it may signal a need for further monitoring or testing. A measurement below the 3rd percentile is commonly defined as microcephaly. This condition suggests the brain may not have developed properly in the womb or has stopped growing at the expected rate. Microcephaly can be associated with various causes, including infectious, genetic, or toxic origins.
Conversely, a head circumference above the 97th percentile is referred to as macrocephaly. This suggests the baby’s head is unusually large for their age and sex. Macrocephaly can result from several conditions, such as hydrocephalus or a benign, inherited trait known as familial macrocephaly.
Expected Head Growth After the First Month
Following the initial measurement, the newborn’s head enters a period of intense growth. The first four months after birth mark the fastest rate of head growth the child will experience. On average, the head circumference increases by about 2 cm per month during the first three months of life. This rapid expansion is a direct result of the brain’s swift post-natal development.
This growth rate slows down, increasing by approximately 1 cm per month between three and six months of age. Regular measurements, typically continuing up to 24 to 36 months, ensure that the growth remains smooth and follows the appropriate curve for the child.