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Microcephaly & Other Birth Defects

Zika and Microcephaly

Graphic of doctor with a pregnant woman

Microcephaly is a birth defect in which a baby’s head is smaller than expected when compared to babies of the same sex and age. Babies with microcephaly often have smaller brains that might not have developed properly.

Zika virus infection during pregnancy is a cause of microcephaly. During pregnancy, a baby’s head grows because the baby’s brain grows. Microcephaly can occur because a baby’s brain has not developed properly during pregnancy or has stopped growing after birth.

Congenital Zika Syndrome

Congenital Zika syndrome is a pattern of birth defects found among fetuses and babies infected with Zika virus during pregnancy. Congenital Zika syndrome is described by the following five features:

  • Severe microcephaly where the skull has partially collapsed
  • Decreased brain tissue with a specific pattern of brain damage
  • Damage to the back of the eye
  • Joints with limited range of motion, such as clubfoot
  • Too much muscle tone restricting body movement soon after birth

Not all babies born with congenital Zika infection will have all of these problems. Some infants with congenital Zika virus infection who do not have microcephaly at birth may later experience slowed head growth and develop postnatal microcephaly. 

Recognizing that Zika is a cause of certain birth defects does not mean that every pregnant woman infected with Zika will have a baby with a birth defect. It means that infection with Zika during pregnancy increases the chances for these problems. Scientists continue to study how Zika virus affects mothers and their children to better understand the full range of potential health problems that Zika virus infection during pregnancy may cause.

Future Pregnancies

Based on the available evidence, we think that Zika virus infection in a woman who is not pregnant would not pose a risk for birth defects in future pregnancies after the virus has cleared from her blood. From what we know about similar infections, once a person has been infected with Zika virus, he or she is likely to be protected from a future Zika infection.

Related Resources

What to know: If your doctor suspects microcephaly during pregnancy

What to know: If your baby was born with congenital Zika syndrome

What to know: If your baby may have been affected by Zika but has no related health conditions at birth

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