At each of your newborn's well-baby visits, your pediatrician will use a measuring tape to measure their head size or head circumference (HC). Measuring your baby's head circumference is an easy, non-invasive way for a pediatrician to monitor your baby's growth and development, which is an important indicator of health. Learning more about the average newborn head circumference and how your baby's head compares to that number can help you to make sense out of this part of infant development.
How and Why Your Baby's Head Size is Measured
The brains of babies and toddlers grow rapidly in the first three years of life, according to the Centers for Disease Control and Prevention (CDC). Until your baby turns two, head circumference measurement will be a routine part of every well-baby appointment.
Head Circumference Measurement Process
Head circumference is taken by measuring the size of the head around the largest area. This measures the distance from above the eyebrows and ears to the back of the head. Your pediatrician will use a growth chart to log your baby's head size to compare it to previous measurements of your baby's head circumference. The doctor may also compare it to the average newborn head circumference (the normal, expected ranges of a baby's head size based on their age and sex).
For example, if your boy baby is 3.5 months old and has a head circumference of 41.7 centimeters, they are in the 50th percentile, according to data compiled by the Centers for Disease Control and Prevention (CDC). If that baby is 6.5 months old, their head should measure about 44cm to be in the 50th percentile.
Growth Charts and Percentiles
The Infant Head Circumference Chartoffers an online growth chart calculator that shows how your baby's head circumference compares to other babies of the same age and sex. Pediatricians often refer to growth percentiles as they monitor a child's development. This data is typically shown as a curved pattern of lines on a chart.
Your child's pediatrician will use the growth chart to track the growth pattern of your child. As your little one grows, the pediatrician will refer to your child's previous percentiles to ensure they are on track with their individual growth pattern. For example, if your child's head measurement was always in the 50th percentile but suddenly shifted down to 35th percentile, their pediatrician may order imaging scans and other diagnostic tests to look for potential health problems.
Comparing to the Average Baby Head Circumference
Keep in mind that there are several things that might lead you to believe your baby's head is larger or smaller than average. If you measure at home, you might not measure in the correct place. And there are some tape measures that are more accurate than others. Always reach out to your pediatrician if you have concerns. Your baby's head size may be an indicator of a particular health issue, but it may also just mean that your baby has a slightly larger or smaller head.
Larger Than Average Infant Head Circumference
If your baby has a larger than normal head size, it may be because large heads run in the family. But it can also signal other concerns.
Macrocephaly is the term used to describe an infant head circumference that is larger than average. About 5% of infants have macrocephaly. Sometimes, macrocephaly can be a sign of an underlying health condition.
To be on the safe side, your pediatrician may refer your baby to a pediatric neurosurgeon, who will provide a physical and neurological examination of your baby and may order imaging tests to determine the cause.
Smaller Than Average Infant Head Circumference
Microcephaly describes a smaller than average infant head circumference. Microcephaly is uncommon. In the United States, approximately 1 in every 800-5,000 babies are born with smaller than expected heads.
In some cases, microcephaly occurs due to genetic mutations. Certain infections during pregnancy, exposure to harmful substances in utero, severe malnutrition, and an interruption of blood supply to the baby's brain may also cause microcephaly. A Zika virus infection during pregnancy can also be a cause of microcephaly.
Some babies don't experience any problems due to their small head size. Others may have developmental delays throughout infancy and childhood, and others may have underlying health conditions that require treatment.
Head Size and Autism Risk
Some studies suggest that babies with larger head sizes may have an increased risk of autism. Many of the babies with large heads who were later diagnosed with autism were also found to have unusually large brains. But not all researchers agree.
Other study findings say there is no evidence to suggest that larger-than-average head sizes are connected to autism. These mixed findings suggest further research is needed to explore the link between infant head size and autism spectrum disorder.
Head Size and Intelligence
If your baby has a bigger head size, he or she may also have a bigger brain. However, a bigger head and brain doesn't necessarily mean your baby is a genius.
One study published in the Journal of Molecular Psychiatry found that there were significant associations infant head circumference and cognitive ability. However, the researchers found 17 genes that influence cognitive skills, brain size, and body shape.This suggests that it's genetics that play a role in a baby's intelligence, not their head size.
Monitoring Your Baby's Head Size
Infant head size is a good indicator of health and can help pediatricians detect potential problems. Your baby's pediatrician will measure their head circumference at each of their well-baby visits. If you choose, you can measure your baby's head circumference at home using a non-elastic measuring tape. If you are concerned about your baby meeting his or her developmental milestones or their head size, talk to your pediatrician.