CDC Report: Zika Virus Poses Greater Risk of Birth Defects Than Previously Thought

10% to 15% of pregnancies are affected

Women who develop Zika virus infection (ZVI) during pregnancy have a one-in-10 chance of having a fetus or infant with virus-associated birth defects, and this rate can increase to 15% if the infection occurs during the first trimester, according to a report from the Centers for Disease Control and Prevention (CDC). The findings, published in the April 4 issue of Morbidity and Mortality Weekly Report (MMWR), indicate that ZVI may pose a greater risk during pregnancy than previously thought.

The MMWR article includes an analysis of completed pregnancies (including live births and pregnancy losses, regardless of gestational age) in the 50 U.S. states and the District of Columbia with laboratory evidence of possible recent ZVI reported to the U.S. Zika Pregnancy Registry (USZPR) from January 15 to December 27, 2016. Birth defects potentially associated with ZVI during pregnancy include brain abnormalities and/or microcephaly, eye abnormalities, other consequences of central nervous system dysfunction, and neural tube defects and other early brain malformations.

During the analysis period, a total of 1,297 pregnancies with possible recent ZVI were reported to the USZPR from 44 states, including 972 completed pregnancies with reported outcomes (895 live-born infants and 77 pregnancy losses). Among the completed pregnancies, 599 (62%) pregnant women were asymptomatic; 348 (36%) were symptomatic; and 25 (3%) had missing symptom information.

Birth defects were reported for 24 (10%) of the 250 completed pregnancies with laboratory-confirmed recent ZVI.

Birth defects occurred in a higher proportion of fetuses and infants whose mothers were infected during the first trimester of pregnancy. Among 157 pregnancies in which women had symptom onset or exposure to ZVI during the first trimester, 14 (9%) fetuses and infants had reported birth defects. When pregnancies with symptom onset or exposure during the first trimester were limited to those with laboratory-confirmed ZVI, nine (15%) of 60 completed pregnancies had reported birth defects.

According to the article, the proportion of fetuses and infants with birth defects among pregnancies with confirmed ZVI at any time during pregnancy was more than 30 times higher than the baseline prevalence in the pre-Zika years.

“These findings underscore the serious risk for birth defects posed by Zika virus infection during pregnancy, and highlight why pregnant women should avoid Zika virus exposure and that all pregnant women should be screened for possible Zika virus exposure at every prenatal visit, with testing of pregnant women and infants in accordance with current guidance,” the article states.

The CDC recommends Zika virus testing for all infants born to women with laboratory evidence of ZVI during pregnancy, and for infants with findings that suggest congenital Zika syndrome born to women with an epidemiologic link suggesting possible transmission, regardless of maternal testing results. Infants without abnormalities born to women with an epidemiologic link suggesting possible Zika virus exposure during pregnancy, and for whom maternal testing was not performed or was performed more than 12 weeks after exposure, should have a comprehensive exam. If there is concern about infant follow-up or if maternal testing is not performed, infant Zika virus testing should be considered.

The initial evaluation of infants should include a comprehensive physical examination, including a neurological examination, postnatal neuroimaging, and a standard newborn hearing screen.

Source: MMWR; April 4, 2017.