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What is Microcephaly?

There is a good reason your child’s pediatrician measures your baby’s head circumference at each check-up. A baby’s head typically grows in a very predictable pattern that can be followed on a standardized growth chart. However, when a baby’s head grows at an abnormally slow rate, or the head circumference is small to begin with, it is known as microcephaly.

Microcephaly essentially means that the skull growth is not keeping up with the growth in the rest of the body. Typically, a small skull indicates a small brain. The smaller the head, the more likely that brain development will not be normal, and the baby will show signs of developmental delay.

There is no single disease that causes microcephaly. Instead, this disorder may result from any injury to the brain that disrupts its growth. Anything that causes brain injury before or after birth can lead to microcephaly. Common causes before birth include prenatal maternal infections or diseases, in utero drug exposure, metabolic disorders, and genetic abnormalities. Other causes after birth include head trauma or meningitis/encephalitis.

There are approximately 25,000 babies born annually in the United States with microcephaly. Sometimes brain imaging with a CT scan or MRI can be useful in detecting other abnormalities if the baby shows signs of developmental delay. Genetic testing may be done, especially if there are other abnormal findings on the baby’s physical exam.

Sometimes, specific blood tests will be used to look for the most common infections that cause microcephaly. These infections include toxoplasmosis, rubella, CMV, syphilis, and herpes. More recently, researchers have begun to suspect that the Zika virus is also a cause of microcephaly because there has been a dramatic spike in the number of cases in Zika-prone areas.

Other problems often go along with microcephaly, including seizures, developmental abnormalities, cerebral palsy, and eye/vision problems. Often babies with this condition will need to be evaluated by a pediatric neurologist, infectious disease specialist, ophthalmologist, and/or geneticist, in addition to regular visits with the pediatrician for routine head circumference measurements.

The prognosis for microcephaly depends on the underlying cause. Children who have an associated genetic problem or microcephaly due to a prior intrauterine infection tend to have a poorer prognosis.


  • American Academy of Pediatrics
  • Microcephaly.
  • Microcephaly in infants and children: etiology and evaluation.
    American Academy of Neurology
  • Practice Parameter: Evaluation of the child with microcephaly.

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