Microcephaly (my-kroh-SEF-uh-lee) is a rare neurological condition in which an infant's head is much smaller than the heads of other children of the same age and sex. Sometimes detected at birth, microcephaly often occurs when there is a problem with brain development in the womb or when the brain stops growing after birth.

Microcephaly can be caused by a variety of genetic and environmental factors. Children with microcephaly often have developmental issues. Although there's no treatment for microcephaly, early intervention with speech, occupational and other supportive therapies may help enhance a child's development and improve quality of life.


The primary symptom of microcephaly is having a head size that is much smaller than that of other children of the same age and sex.

Head size is a measure of the distance around the top of the child's head (circumference). Using standardized growth charts, health care providers compare the measurement with other children's measurements in percentiles.

Some children just have small heads, with a measurement that falls below an established value for children of the same age and sex. In children with microcephaly, head size measures much smaller than average for the child's age and sex.

A child with more-severe microcephaly may also have a sloping forehead.

When to see a doctor

Chances are your health care provider will detect microcephaly at your baby's birth or at a regular well-baby checkup. However, if you think your baby's head is small for the baby's age and sex or isn't growing as it should, talk to your provider.


Microcephaly usually is the result of a problem with brain development, which can occur in the womb (congenital) or during infancy. Microcephaly may be genetic. Other causes may include:

  • Craniosynostosis (kray-nee-o-sin-os-TOE-sis). Early fusing of the joints (sutures) between the bony plates that form an infant's skull keeps the brain from growing. Treating craniosynostosis usually means an infant needs surgery to separate the fused bones. This surgery relieves pressure on the brain, giving it enough space to grow and develop.
  • Genetic changes. Down syndrome and other conditions may result in microcephaly.
  • Decreased oxygen to the fetal brain (cerebral anoxia). Certain complications of pregnancy or delivery can impair oxygen delivery to a baby's brain.
  • Infections passed to the fetus during pregnancy. These include toxoplasmosis, cytomegalovirus, German measles (rubella), chickenpox (varicella) and Zika virus.
  • Exposure to drugs, alcohol or certain toxic chemicals in the womb. Any of these may affect fetal brain development during pregnancy.
  • Severe malnutrition. Not getting enough nutrients during pregnancy may hurt fetal brain development.
  • Uncontrolled phenylketonuria (fen-ul-kee-toe-NU-ree-uh), also known as PKU, in the mother. phenylketonuria (PKU) hampers the mother's ability to break down the amino acid phenylalanine and may affect brain development of the fetus during pregnancy.


Some children with microcephaly achieve developmental milestones even though their heads will always be small for their age and sex. But depending on the cause and severity of the microcephaly, complications may include:

  • Developmental delays, including speech and movement
  • Difficulties with coordination and balance
  • Dwarfism or short stature
  • Facial distortions
  • Hyperactivity
  • Intellectual delays
  • Seizures


Learning your child has microcephaly can raise questions about future pregnancies. Work with your health care provider to determine the cause of the microcephaly. If the cause is genetic, you may want to talk to a genetics counselor about the risk of microcephaly in future pregnancies.

May 26, 2022

  1. Safier RA, et al., eds. Neurology. In: Zitelli and Davis' Atlas of Pediatric Physical Diagnosis. 8th ed. Elsevier; 2023. https://www.clinicalkey.com. Accessed March 13, 2022.
  2. Boom JA. Microcephaly in infants and children: Etiology and evaluation. https://www.uptodate.com/home. Accessed March 13, 2022.
  3. Facts about microcephaly. Centers for Disease Control and Prevention. https://cdc.gov/ncbddd/birthdefects/microcephaly.html. Accessed March 26, 2022.
  4. Microcephaly information page. National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/Disorders/All-Disorders/Microcephaly-Information-Page. Accessed March 13, 2022.
  5. AskMayoExpert. Craniosynostosis and positional plagiocephaly (infant). Mayo Clinic; 2022.
  6. Nielsen-Saines K. Congenital Zika virus infection: Clinical features, evaluation, and management of the neonate. https://www.uptodate.com/contents/search. Accessed March 13, 2022.
  7. Hoecker JL (expert opinion). Mayo Clinic. April 1, 2022.


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