In the U.S. territories, 5% of women who had confirmed Zika virus infection (ZVI) during pregnancy had a baby or fetus with ZVI-associated birth defects, according to a report in the Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report. Among women with confirmed ZVI during the first trimester, 8% (nearly one in 12) had a baby or fetus with ZVI-associated birth defects. This report, the first from the U.S. territories, represents the largest number of completed pregnancies with laboratory confirmation of ZVI 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, MD. “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 ZVI who completed their pregnancies, of whom 1,508 had confirmed ZVI. In this cohort, more than 120 pregnancies resulted in ZVI-associated birth defects. The data reported to the Zika pregnancy and infant registries came 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 those of a recent CDC report of primarily travel-associated ZVI in the 50 U.S. states and the District of Columbia, which showed that 5% of completed pregnancies with possible ZVI resulted in an infant with a possible ZVI-associated birth defect. Among those with confirmed ZVI, 8% of first-trimester infections in the U.S. territories resulted in Zika-associated birth defects compared with 15% in the U.S. states and the District of Columbia; these estimates are based on relatively small numbers and are not statistically different. The estimates represent a snapshot in time, the CDC says, 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.

The new analysis of completed pregnancies is the first to identify sufficient numbers of ZVIs during the second and third trimesters of pregnancy to develop preliminary estimates of the risk for each trimester. Among pregnant women in U.S. territories with confirmed ZVI, the proportion affected by Zika-associated birth defects varied by the trimester of diagnosis of ZVI: 8% in first trimester, 5% in the second trimester, and 4% in the 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 ZVI in the U.S. territories, 59% of infants were tested for ZVI at birth. Of the 2,464 live-born infants, 52% received recommended head imaging and 79% had a reported hearing screening at birth.

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

The CDC continues to encourage women and their partners who are living in or traveling to areas with risk of Zika and who are considering pregnancy to talk with their health care providers so that they know the risks of and ways to prevent exposure. The CDC has published updated clinical guidance for health care providers who are caring for pregnant women, babies, and children with possible ZVI.

Source: CDC; June 8, 2017.