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Data & Statistics

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%

About 2 in 20 (10%) babies of women with confirmed Zika virus infection during pregnancy in US states and about 1 in 20 (5%) in US territories had Zika-associated birth defects. 1, 2

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 first 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 first 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 first trimester,
    • slightly more than 1 in 25 (5%) in the second trimester,
    • and 1 in 25 (4%) in the third 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 compared to those who did not experience symptoms. 2,3

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.3
  • In the US territories, about 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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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.mm6613e1
  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.mm6623e1
  3. 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
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