The proportion of Zika-affected pregnancies with birth defects is approximately 20-fold higher compared with the proportion of pregnancies seen in 2013-2014, which is before Zika was introduced into the Americas, according to an article published today in CDC’s Morbidity and Mortality Weekly Report.


The types of birth defects—including brain abnormalities and/or microcephaly, neural tube defects and other early brain malformations, eye defects, and other central nervous system (CNS) problems—were seen in about 3 of every 1,000 births in 2013-2014. In 2016, the proportion of infants with these same types of birth defects born to women with Zika virus infection during pregnancy was about 6% or nearly 60 of every 1,000 completed pregnancies with Zika infections.

The researchers analyzed 2013-2014 data from three birth defects surveillance programs in the United States (Massachusetts, North Carolina, and Georgia) to provide the baseline frequency for Zika-related birth defects. To assess the effect of Zika virus infection during pregnancy, the scientists compared that 2013-2014 baseline number with previously published numbers among pregnancies with Zika virus infection from the US Zika Pregnancy Registry (USZPR) from 2016.

They identified 747 infants and fetuses with one or more of these defects from programs in Massachusetts, North Carolina, and Georgia, from 2013-2014. Brain abnormalities and/or microcephaly were the most frequent conditions reported.  Data from the USZPR identified 26 infants and fetuses with these same birth defects among the 442 completed pregnancies of women with possible Zika infection from January through September 2016. These findings demonstrate the importance of having monitoring systems that collect data on birth defects.

CDC supports state, territorial, tribal and local health departments to establish or enhance surveillance systems that rapidly collect information about birth defects that have been observed with Zika virus infection during pregnancy. Today, five additional jurisdictions—Arkansas, Nebraska, Nevada, the Federated States of Micronesia, and the Republic of the Marshall Islands— were awarded funding, bringing the total to 50 jurisdictions and more than $27 million in support of birth defects surveillance for fiscal years 2016 and 2017.

CDC continues to recommend that pregnant women not travel to areas with Zika. If a pregnant woman must travel to or lives in an area with Zika, she should talk with her healthcare provider and strictly follow steps to prevent mosquito bites and sexual transmission of Zika virus. Pregnant women with possible exposure to Zika virus should be tested for Zika infection even if they do not have symptoms.