CDC analysis of data from US territories finds serious birth defects in about 1 in 12 fetuses or infants of pregnant women with Zika infection in the first trimester

In the U.S. territories, 5 percent of women who had confirmed Zika virus infection during pregnancy had a baby or fetus with Zika virus-associated birth defects, according to a report published today in CDC’s Morbidity and Mortality Weekly Report. Among the women with confirmed Zika infection during the first trimester, 8 percent or nearly 1 in 12 had a baby or fetus with Zika virus-associated birth defects. This report, the first from the US territories, represents the largest number of completed pregnancies with laboratory confirmation of Zika virus infection to date.

“As these latest findings illustrate, Zika virus poses a serious threat to pregnant women and their babies, regardless of when the infection occurs during the pregnancy,” said CDC Acting Director Anne Schuchat, M.D. “Women in the U.S. territories and elsewhere who have continued exposure to mosquitoes carrying Zika are at risk of infection. We must remain vigilant and committed to preventing new Zika infections.”

The report reviewed the cases of 2,549 women with possible Zika virus infection who completed their pregnancies, of which 1,508 had confirmed Zika virus infection. In this report, more than 120 pregnancies resulted in Zika-associated birth defects. The data reported to the Zika pregnancy and infant registries were from American Samoa, the Commonwealth of Puerto Rico, the Federated States of Micronesia, the Republic of Marshall Islands, and the U.S. Virgin Islands from January 1, 2016, to April 25, 2017. 

These findings from U.S. territories are consistent with a recent CDC report of primarily travel-associated Zika virus infections from the 50 U.S. states and the District of Columbia showing that 5 percent of completed pregnancies with possible Zika virus infection resulted in an infant with a possible Zika virus-associated birth defect. Among those with confirmed infection, eight percent of first-trimester infections from the US territories resulted in Zika-associated birth defects compared to 15 percent in the U.S. states and District of Columbia; these estimates are based on relatively small numbers and are not statistically different. The estimates represent a snapshot in time and the Zika pregnancy and infant registries, along with prospective cohort studies, will continue to provide essential data to better understand the magnitude of the risk of Zika infection during early pregnancy.

“This report highlights the threat of Zika virus infection in pregnancy, particularly the risk of damage to the baby’s brain,” said Peggy Honein, Ph.D., co-lead, Pregnancy and Birth Defects Task Force, CDC Zika Response. “To help us fully understand and plan for Zika’s effect, we must continue to monitor babies for any problems with vision, hearing, or other disabilities.”

Zika virus infection during any stage of pregnancy can cause birth defects

This is the first report of completed pregnancies with sufficient numbers of Zika virus infections identified during the second and third trimesters of pregnancy to develop preliminary estimates of risk for each trimester. Among pregnant women in U.S. territories with confirmed Zika virus infection, the proportion affected by Zika-associated birth defects varied by trimester of diagnosis of Zika infection: 8 percent in first trimester, 5 percent in second trimester, and 4 percent in third trimester.

The report also describes how many infants received recommended testing and evaluation according to CDC guidance. Based on data reported to the Zika pregnancy and infant registries for infants born to women with laboratory evidence of recent possible Zika virus infection in the U.S. territories, 59 percent of infants were tested for Zika virus infection at birth. Of the 2,464 live-born infants, 52 percent were reported to have received recommended head imaging and 79 percent had a reported hearing screening at birth.

This report reinforces earlier guidance that preventing Zika virus infection at any time during pregnancy is critically important given the severity of its associated birth defects. Pregnant women living in areas with ongoing local Zika virus transmission are at continued risk of developing infection.

The findings in this report also emphasize the importance of follow-up care for infants with congenital Zika virus infection. Identification of infants born to mothers with Zika virus infection during pregnancy allows for timely planning of intervention services. In addition, assessing diagnostic testing and clinical evaluation practices can help CDC, public health officials, and healthcare providers direct efforts to monitor and provide care for infants affected by Zika virus.

CDC continues to encourage women and their partners considering pregnancy who live in or travel to areas with risk of Zika to talk to their healthcare providers so that they know the risks and ways to prevent exposure. CDC has published updated clinical guidance for healthcare providers caring for pregnant women, babies, and children with possible Zika virus infection.

To learn more about Zika virus, visit https://www.cdc.gov/zika/. Healthcare providers can visit https://www.cdc.gov/zika/hc-providers/index.html for CDC’s latest clinical guidance, testing, and training information for Zika.

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U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES