Microcephaly is a condition in which a person's head size is much smaller than that of others of the same age and sex. Head size is measured as the distance around the top of the head. A smaller than normal size is determined using standardized charts.
Microcephaly most often occurs because the brain does not grow at a normal rate. The growth of the skull is determined by brain growth. Brain growth takes place while a baby is in the womb and during infancy.
Conditions that affect brain growth can cause smaller than normal head size. These include infections, genetic disorders, and severe malnutrition.
Genetic conditions that cause microcephaly include:
Other problems that may lead to microcephaly include:
Becoming infected with the Zika virus while pregnant can also cause microcephaly. The Zika virus is present in Brazil and other parts of South America, along with Mexico, Central America, and the Caribbean.
Most often, microcephaly is diagnosed at birth or during routine well-baby exams. Talk to your health care provider if you think your infant's head size is too small or not growing normally.
Call your provider if you or your partner has been to an area where Zika is present and you are pregnant or thinking about becoming pregnant.
Most of the time, microcephaly is discovered during a routine exam. Head measurements are part of all well-baby exams for the first 18 months. Tests take only a few seconds while the measuring tape is placed around the infant's head.
The provider will keep a record over time to determine:
It may also be helpful to keep your own records of your baby's growth. Talk to your provider if you notice that the baby's head growth seems to be slowing down.
If your provider diagnoses your child with microcephaly, you should note it in your child's personal medical records.
Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.