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What is microcephaly?

Microcephaly is a medical condition in which the circumference of the head is smaller than normal because the brain has not developed properly, or has stopped growing. Microcephaly can be present at birth or it may develop in the first few years of life. It is most often caused by genetic abnormalities that interfere with the growth of the cerebral cortex during the early months of fetal development. It is associated with Down's syndrome, chromosomal syndromes and neurometabolic syndromes. Babies may also be born with microcephaly if, during pregnancy, their mother abused drugs or alcohol; became infected with a cytomegalovirus, rubella (German measles), varicella (chicken pox) virus or possibly Zika virus; was exposed to certain toxic chemicals; or had untreated phenylketonuria (PKU). Babies born with microcephaly will have a smaller than normal head that will fail to grow as they progress through infancy.

With viral-induced brain injury, such as with the Zika virus, there is often widespread tissue and cell death leading to brain shrinkage rather than simply impaired growth. The Zika virus is also associated with retinal lesions in about a third of cases, often leading to blindness.

Depending on the severity of the accompanying syndrome, children with microcephaly may have mental retardation, delayed motor functions and speech, facial distortions, dwarfism or short stature, hyperactivity, seizures, difficulties with coordination and balance, and other brain or neurological abnormalities. Some children with microcephaly will have normal intelligence and a head that will grow bigger, but they will track below the normal growth curves for head circumference.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

Microcephaly is when a baby’s head is much smaller than expected. Normally, the head grows because the brain grows. With microcephaly, it could be that the brain hasn’t developed, and therefore the head doesn’t grow. Microcephaly can occur on its own, or it can be associated with other major birth defects.

Dr. Sanjay Gupta, MD
Fitness Specialist

Strictly defined, microcephaly means “small head." "Micro" just means small and “cephaly” refers to the head. In microcephaly, babies’ heads and their brains do not develop properly during the time that they are developing. It means that certain cells in the brain didn’t move to areas where they should have and, as a result, the brain and skull didn’t grow to their normal size. So, the baby has a very small head, and a small brain that is not developed properly.

There's a whole wide range of microcephaly and it can be, in certain people, more of a cosmetic sort of thing but it really depends on why microcephaly developed. If the Zika virus causes the problem in the brain and the central nervous system such that the brain and head are small, it can potentially be a lethal problem.

Microcephaly is a birth defect in which a baby’s head is smaller than expected, compared to babies of the same sex and age. Babies with mild microcephaly often don’t have problems other than small head size. Babies with severe microcephaly may have lifelong health problems, including intellectual and developmental disabilities.

We don’t know for sure what causes microcephaly in most babies, but these things may cause microcephaly in some babies:

  • Gene changes (also called mutations) or chromosomal conditions
  • Being exposed to alcohol or certain drugs or chemicals in the womb
  • Being exposed to certain infections in the womb, including Zika virus, chickenpox (also called varicella), rubella (also called German measles), toxoplasmosis or cytomegalovirus
  • Brain problems, like cerebral anoxia, craniosynostosis or traumatic brain injury
  • Metabolism or nutrition problems

Learn more at marchofdimes.org/microcephaly

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.