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:
Use of certain drugs during pregnancy, especially alcohol and phenytoin
When to Contact a Medical Professional
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.
What to Expect at Your Office Visit
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 health care provider will keep a record over time to determine:
What is the head circumference?
Is the head growing at a slower rate than the body?
What other symptoms are there?
It may also be helpful to keep your own records of your baby’s growth. Talk to your health care provider if you notice that the baby’s head growth seems to be slowing down.
If your health care provider diagnoses your child with microcephaly, you should note that in your child's personal medical records.
Kinsman SL, Johnston MV. Congenital anomalies of the central nervous system. In: Kliegman RM, Stanton BF, St. Geme JW III, Schor NF, Behrman RE, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 585.10.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.