The head of a newborn baby is notably large compared to the rest of the body, reflecting the rapid development of the brain during gestation. This disproportionate size is characteristic of human growth, known as cephalocaudal development, where the head and brain develop faster than the trunk and limbs. The newborn brain is already about 25% of its future adult weight, requiring a large protective casing at birth. Monitoring head size remains an important part of pediatric care because this rapid growth continues throughout early childhood.
Typical Head Circumference Measurements
The size of a baby’s head is measured by its circumference, a statistic taken immediately after birth to establish a baseline for growth. For a full-term infant, the average head circumference typically falls between 13 and 14 inches (33 to 37 centimeters). The average measurement is often cited as 13.5 inches (34.2 centimeters).
This measurement is officially known as the Occipitofrontal Circumference (OFC). It is taken by wrapping a measuring tape around the largest diameter of the skull, positioned just above the eyebrows and around the most prominent point at the back of the head. At birth, the head makes up approximately one-fourth of the baby’s total body length, highlighting the resources dedicated to early brain growth.
How the Head Adapts During Delivery
Despite its size, the newborn skull is designed with remarkable flexibility to navigate the narrow passage of the birth canal during a vaginal delivery. The skull is not a single fused bone but rather several bony plates—including the frontal, parietal, and occipital bones—connected by fibrous joints called sutures. These sutures are not rigid and allow the bone plates to move relative to one another.
Where these sutures intersect are wider gaps of connective tissue known as fontanelles, or soft spots, which are covered by a tough membrane. The two most prominent are the diamond-shaped anterior fontanelle at the top front of the head and the smaller, triangle-shaped posterior fontanelle toward the back. This structure provides the necessary plasticity for the head to compress and change shape during labor.
The process of the head temporarily changing shape during delivery is called molding, or cephalic molding. As the head is subjected to the intense, sustained pressure of the uterine contractions and the resistance of the birth canal, the soft skull plates slide and sometimes overlap at the suture lines. This allows the head to become narrower and longer, effectively reducing its overall diameter to pass through the pelvis.
The resulting appearance immediately after a vaginal delivery is often an elongated or cone-shaped head, which can cause concern for new parents. This altered shape is a normal and temporary consequence of the successful passage through the birth canal. The bones naturally spring back to a more rounded shape as the pressure is released. This temporary molding usually resolves on its own within a few days to a week after birth.
Head Size as a Key Indicator of Health
A baby’s head circumference is routinely tracked by healthcare providers because it serves as an important proxy for brain development. Since the skull encases the brain, the rate at which the head grows reflects the rate of brain growth, particularly during the first few years of life. Pediatricians plot the Occipitofrontal Circumference (OFC) on standardized growth charts at every well-baby visit.
Tracking this growth trajectory over time is more informative than a single measurement taken at birth. Consistent growth along a percentile line indicates healthy development, while significant deviations signal an underlying health issue that requires investigation. The two primary deviations monitored are microcephaly and macrocephaly.
Microcephaly
Microcephaly occurs when the head circumference is significantly smaller than average, defined as more than two standard deviations below the mean for the baby’s age and sex. This small size indicates that the underlying brain size is also small (micrencephaly). Microcephaly is associated with impaired brain development and may be linked to genetic conditions or prenatal exposures, such as infections.
Macrocephaly
Macrocephaly is defined as a head circumference significantly larger than average, typically more than two standard deviations above the mean. This condition can be caused by an abnormally large brain (megalencephaly) or an increase in the fluid surrounding the brain. A common cause of acquired macrocephaly is hydrocephalus, which involves an excessive buildup of cerebrospinal fluid. Monitoring head size helps ensure that potential issues are identified early, allowing for timely intervention and support.