Why Do Pediatricians Measure Your Baby's Head at Birth?

With a simple measurement of your baby's head, it's possible to detect some important neurological pathologies. Do you know what this involves?

Reviewed and approved by the pediatrician Marcela Alejandra Caffulli.

Written by Marcela Alejandra Caffulli

Last update: 27 December, 2022

The cephalic circumference is the measurement of the baby’s head that’s performed at birth and at each health check-up. The purpose of this practice is to detect alterations in the size of the skull, called microcephaly and macrocephaly.

When the child’s head has an abnormal size, this may be an indication of some disease of the nervous system. It’s important, therefore, to closely monitor the child and evaluate the need for additional studies or to consult other specialists.

In this article, we’ll tell you why the first head circumference measurement is so important.

Why is it important to measure your baby’s head?

The size of a baby’s head at birth gives doctors an idea of how the nervous system developed during gestation.

To better understand this idea, we need to understand what structures make up this system and how it develops in the mother’s womb.

Anatomy of the central nervous system (CNS)

The central nervous system is made up of several structures, among which we can highlight the following:

• The cerebrum
• The cerebellum, brainstem, spinal cord
• Cerebrospinal fluid (circulating in cisterns or ducts)
• The skull (bones and cartilage)

Fetal central nervous system development

In those cases in which the brain suffers some alteration and doesn’t develop properly, this will also affect the growth of the bones of the head. For example, when the mother acquires a certain infection during pregnancy, the baby may be born with a smaller skull than usual. This is known as microcephaly.

In turn, some type of obstruction may occur in the system of ducts that carry the cerebrospinal fluid, which will cause this content to accumulate in the area before the blockage and place pressure on other structures.

Indirectly, this will cause a “stretching” of the cranial cavity and as a consequence, the baby will be born with a skull that’s larger than normal. This is known as macrocephaly.

In both cases, the baby will be born with an abnormal head circumference, and although this is not a problem in itself, it indicates that some alteration occurred during fetal neurological development.

How do doctors measure the baby’s head and why?

Head circumference is a simple measurement of the perimeter of the baby’s head. Doctors use a soft tape measure, which they place around the skull in the area of greatest circumference. This is located at the level of the forehead (front), temples (sides), and occiput (back).

Ideally, doctors should perform the procedure with the baby’s head upright. However, as this is very difficult to achieve in newborns, they take it with the baby lying on its back on the examination table.

Although many infants cry during the first examination in the delivery room, this isn’t an indication of any risk or physical ailment.

The importance of performing this measurement in the first 24 hours after birth is to be able to indirectly evaluate how the central nervous system developed in utero.

It’ll also alert us to any possibility of syndromic congenital diseases (those consisting of several defects), such as Down syndrome.

The size of the baby’s head

Head circumference, weight, and length (height) are part of the baby’s “intrauterine history”. These measurements will allow us to deduce whether the baby was exposed to any risk factors for disease and to act accordingly.

To find out if the baby was born with a head of adequate size or not, we should always refer to the corresponding growth charts. In these charts, we find the measurement data of hundreds of children from different parts of the world, which has allowed us to estimate the average growth for each age and sex.

When we measure the baby’s head circumference, we must compare this data with the tables and define the percentile where the child is. This way, we’ll be able to tell if the baby has an average-sized skull or not.

We’ll now define the 3 possibilities:

• Normocephalic: When the head circumference percentile is between 3 and 97
• Microcephalic: When the percentile is below 3
• Macrocephalic: When the percentile is above 97

Possible problems

Microcephaly and macrocephaly can occur for a variety of reasons. These can include problems that directly affect brain growth (called primary defects) or cause changes in head circumference for other reasons (called secondary defects).

Causes of microcephaly

The most common causes of neonatal microcephaly include the following:

• Genetic syndromes, such as Down, Edwards, or Patau Syndrome
• Primary brain development defects
• Perinatal infections, such as chickenpox, toxoplasmosis, or rubella
• Zika virus
• Exposure to toxins or radiation during gestation
• Severe intrauterine malnutrition

Causes of macrocephaly

The following are the most frequent causes of neonatal macrocephaly:

• Familial macrocephaly
• Genetic brain malformations
• Sotos syndrome
• Achondroplasia
• Neurofibromatosis
• Hematomas, cysts, or cerebral hemorrhages
• Congenital hydrocephalus
• Encephalic tumors

About the importance of measuring a baby’s head

Doctors obtain the head circumference by measuring a baby’s head. It allows them to infer whether the brain developed correctly in utero.

It’s a simple, inexpensive, minimally invasive, and painless strategy for the early detection of important pathologies in newborns. In addition, it will sometimes raise the alert about the possibility of other associated defects, such as those that are part of syndromes.

Measuring head circumference at birth is very important, but it’s something that should take place each subsequent health check-up as well. Some pathologies are evolutionary and require a long time to manifest themselves. With this simple measurement, we can detect them before they become a problem that’s difficult to solve.