Microcephaly is a birth defect in which a baby’s head size is smaller than expected when compared to other babies of the same age and sex. Severe microcephaly is a more serious form of the condition in which a baby’s head size is much smaller when compared to other babies of the same age and sex. In babies with microcephaly, often the brain has not developed properly.

regular headsize
severe microcephaly

Photo Credit: Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilites


Zika Virus, Pregnancy and Microcephaly

Zika virus infection during pregnancy can cause microcephaly and other birth defects. If you are pregnant, or trying to become pregnant, do not travel to a Zika-affected area. If you are pregnant and you or your sex partner has traveled to a Zika-affected area, contact your health care provider to discuss Zika testing and ongoing prevention against Zika virus infection. Ask your provider if you need additional ultrasound tests because you may have been infected with the Zika virus.


Causes and Risk Factors

Most of the time, the cause of microcephaly is unknown. Sometimes however, certain exposures during pregnancy can cause microcephaly, including:

  • Certain infections, such as Zika virus, rubella, toxoplasmosis or cytomegalovirus
  • Severe malnutrition, meaning a lack of nutrients or not getting enough food
  • Exposure to harmful substances such as alcohol, certain drugs or toxic chemicals
  • Interruption of the blood supply to the baby’s brain during development


Microcephaly can sometimes be diagnosed during pregnancy with an ultrasound test. To diagnose microcephaly after birth, a health care provider will measure the baby’s head circumference (the distance around the baby’s head) and compare the measurement to population standards by sex and age.

Possible Problems

It is difficult to predict what problems a baby may have due to microcephaly. Some babies with mild microcephaly have no problems apart from small head size. However, if an infant’s microcephaly is the result of poor brain development during pregnancy, or if it is linked to other deformities, there may be multiple medical problems. A baby with microcephaly may have:

  • Seizures
  • Problems with sitting, standing, walking or speaking
  • Learning or intellectual disabilities (reduced ability to learn and function in daily life)
  • Problems with movement and balance
  • Feeding problems, such as difficulty swallowing
  • Hearing loss
  • Vision problems

These issues can range from mild to serious. Babies with severe microcephaly can experience a greater number of complications, or struggle more with them, than babies with milder microcephaly. Rarely, severe microcephaly can be fatal.

Caring for a Child with Microcephaly

There is no cure or standard treatment for microcephaly. Babies with microcephaly need regular check-ups with a health care provider to monitor their development and to manage any health complications.

Babies with microcephaly qualify for the New York City Early Intervention Program, which provides evaluations, therapy (such as physical, occupational and speech therapy, and special instruction) and support services to families with children who have disabilities or developmental delays. The program is available at no out-of-pocket cost, regardless of race, ethnicity, income or immigration status.

Additional Resources