Zika virus infection during pregnancy causes birth defects in 5% of babies, study finds

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June 9, 2017

According to a report published today in the Morbidity and Mortality Weekly Report of Centers for Disease Control and Prevention (CDC), 5% of women in the U.S. and its territories who had confirmed Zika virus infection during pregnancy had a baby or fetus with Zika virus-associated birth defects.

This report is the first from the U.S. and its territories and represents the largest number of completed pregnancies with sufficient numbers of laboratory confirmation of Zika virus infection to date, to develop preliminary estimates of risk for each trimester.

“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 data collected between January 1, 2016 and April 25, 2017 from American Samoa, the Commonwealth of Puerto Rico, the Federated States of Micronesia, the Republic of Marshall Islands, and the U.S. Virgin Islands were reported to the Zika pregnancy and infant registries.

The report assessed the cases of 2,549 women with possible Zika virus infection, who had completed their pregnancies. Of this, 1,508 had confirmed Zika virus infection and more than 120 pregnancies resulted in Zika-associated birth defects.

These findings from the U.S. and its territories are consistent with a recent CDC report of Zika virus infections that are primarily related to travel. The data from 50 U.S. states and the District of Columbia show that 5% of completed pregnancies with possible Zika virus infection resulted in the possibility of Zika virus-associated birth defect in the baby.

Among those with confirmed infection, 8% (nearly 1 in 12 women) of first-trimester infections from the U.S. and its territories resulted in Zika-associated birth defects compared with 15% in the U.S. states and the District of Columbia. The estimates are based on relatively small numbers and are not statistically significant, representing a snapshot in time.

The proportion affected by Zika-associated birth defects varies by trimester of diagnosis of Zika infection. Among pregnant women in the U.S. and its territories with confirmed Zika virus infection - 5% in the second trimester and 4% in the third trimester resulted in Zika-associated birth defects. The Zika pregnancy and infant registries, along with prospective cohort studies, will continue to provide necessary data to better understand the extent of Zika infection risk during early pregnancy.

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

“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.”

The report findings also emphasized the importance of follow-up care for babies with congenital Zika virus infection. Identifying infants born to Zika-infected (during pregnancy) mothers allows for timely planning of intervention services. In addition, evaluating diagnostic testing and clinical evaluation practices can help CDC, public health officials, and physicians to focus efforts on monitoring and providing care for Zika-virus-affected babies.

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

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