Data and Statistics on Zika and Pregnancy

Since the Zika virus outbreak in the Americas began in 2015, CDC scientists and clinicians have collaborated to understand the effects of Zika virus infection on the mother and developing baby during pregnancy. There is still much to learn about Zika virus, and CDC continues to study the effects of Zika virus infections to learn how to protect women and their babies.

Proportion with Birth Defects is 5-10%

Among women with confirmed Zika virus infection during pregnancy, Zika-associated birth defects occurred in approximately 2 in 20 (10%) babies born to women in U.S. states and approximately 1 in 20 (5%) babies born to women in U.S. territories. 1, 2

Increase in Birth Defects in Areas with Widespread Local Zika Transmission

The peak of the Zika virus outbreak in areas with widespread local transmission occurred in August 2016.

Six months later, in February 2017, areas with widespread local transmission saw a peak in the number of birth defects linked to Zika virus infection.

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Scientists compared the number of population-level birth defects potentially linked to Zika virus infection from January-March 2017 to January-March 2016
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They found a 4x increase in associated birth defects in areas with widespread local transmission of Zika virus3
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Birth defects potentially linked to Zika virus infection include:
  • Brain abnormalities and/or microcephaly
  • Eye abnormalities
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The highest number of birth defects occurred 6 months after the peak of the Zika virus outbreak

Morbidity and Mortality Weekly Report, Smoots et al. 2020

 States can use this information to plan for referral services and follow-up care for affected infants.

Zika in Early Pregnancy Increases Risk of Birth Defects

Birth defects were reported in a higher proportion of babies whose mothers were infected with Zika virus during the 1st trimester (first three months) of pregnancy.1,2

Bar chart showing higher risk of zika related birth defects when mothers were infected with Zika virus during the first trimester (first three months) of pregnancy. 8 - 15 percent during the first trimester. 5 percent during second and 4 percent during the third trimester.
  • In US states, about 4 in 25 (15%) pregnant women with confirmed Zika virus infection in the 1st trimester had babies with Zika-associated birth defects.1
  • Among pregnant women in US territories with confirmed Zika virus infection, the proportion babies with Zika-associated birth defects varied by trimester of diagnosis of Zika virus infection:
    • 2 in 25 (8%) in the 1st trimester,
    • slightly more than 1 in 25 (5%) in the 2nd trimester,
    • and 1 in 25 (4%) in the 3rd trimester.2

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Symptoms Not Associated With Increased Risk of Birth Defects

The proportion of babies affected by birth defects was similar for women with Zika virus infection during pregnancy who experienced symptoms (e.g. fever, rash, joint pain, or conjunctivitis) compared to those who did not experience symptoms. 2,4

Illustration of a scale showing The proportion of babies affected by birth defects was similar for women with Zika virus infection during pregnancy who experienced symptoms compared to those who did not experience symptoms.
  • In the US states, 2 in 25 (8%), pregnant women with symptoms of Zika virus infection had a baby with Zika-associated birth defects, compared with 3 in 25 (12%) pregnant women without symptoms of Zika virus infection.4
  • In the US territories, approximately 1 in 25 (5%), pregnant women with symptoms of Zika virus infection had a baby with Zika-associated birth defects, compared with about 2 in 25 (7%) pregnant women without symptoms of Zika virus infection.2

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Babies Exposed To Zika Before Birth Might Have Long-Term Health Problems

Some babies with possible Zika infection during pregnancy might look healthy at birth but can develop long-term health problems as they grow. Careful monitoring and evaluation of children born to mothers with evidence of possible Zika virus infection during pregnancy is essential to ensure babies receive the care they need.

In the August 2018 Vital Signs Report, scientists looked at babies who were at least 1 year old born to women with Zika during pregnancy in the U.S. territories. Out of 1,450 babies, approximately 1 in 7 (or 14%) had one or more reported health problems possibly caused by Zika.

Of the 1450 babies at least one year old born to mothers with Zika during pregnancy in the US territories who had some follow-up reported:

References

  1. Reynolds MR, Jones AM, Petersen EE, et al. Vital Signs: Update on Zika Virus–Associated Birth Defects and Evaluation of All U.S. Infants with Congenital Zika Virus Exposure — U.S. Zika Pregnancy Registry, 2016. MMWR Morb Mortal Wkly Rep. 2017;66:366-373. DOI: http://dx.doi.org/10.15585/mmwr.mm6613e1external icon
  2. Shapiro-Mendoza CK, Rice ME, Galang RR, et al. Pregnancy Outcomes After Maternal Zika Virus Infection During Pregnancy — U.S. Territories, January 1, 2016–April 25, 2017. MMWR Morb Mortal Wkly Rep. 2017;66:615-621. DOI: http://dx.doi.org/10.15585/mmwr.mm6623e1external icon
  3. Smoots AN, Olson SM, Cragan J, et al. Population-Based Surveillance for Birth Defects Potentially Related to Zika Virus Infection — 22 States and Territories, January 2016–June 2017. MMWR Morb Mortal Wkly Rep 2020;69:67–71. DOI: http://dx.doi.org/10.15585/mmwr.mm6903a3external icon
  4. Honein MA, Dawson AL, Petersen EE et al. Birth Defects Among Fetuses and Infants of US Women with Evidence of Possible Zika Virus Infection During Pregnancy. JAMA. 2017;317(1):59-68. doi:10.1001/jama.2016.19006
  5. Rice ME, Galang RR, Roth NM, et al. Vital Signs: Zika-Associated Birth Defects and Neurodevelopmental Abnormalities Possibly Associated with Congenital Zika Virus Infection — U.S. Territories and Freely Associated States, 2018. MMWR Morb Mortal Wkly Rep. 2018;67:858-867. DOI: http://dx.doi.org/10.15585/mmwr.mm6731e1external icon.