In findings from what officials call the largest systematic tracking of pregnancies among women with laboratory evidence and confirmation of Zika virus, the U.S. Centers for Disease Control and Prevention released data Tuesday showing that one in 10 women with confirmed infection while pregnant had babies or fetuses with birth defects that have been linked to the disease, including microcephaly, eye abnormalities and spinal malformations.
In findings from what officials call the largest systematic tracking of pregnancies among women with laboratory evidence and confirmation of Zika virus, the U.S. Centers for Disease Control and Prevention released data Tuesday showing that one in 10 women with confirmed infection while pregnant had babies or fetuses with birth defects that have been linked to the disease, including microcephaly, eye abnormalities and spinal malformations. The data represents outcomes of 972 pregnancies, ending in either birth or miscarriage, of women with laboratory evidence of recent Zika infection, in 250 of whom Zika infection was confirmed in further laboratory testing. Birth defects were reported in 51, or 5 percent, of the infants or fetuses resulting from the total number of completed pregnancies in women with evidence of infection, and in 24, or 10 percent, of infants or fetuses whose mothers were confirmed to have recent infection.
The data represents the pregnancy outcomes of women tracked by the United States Zika Pregnancy Registry, which gathers data on pregnancies possibly affected by Zika across the 50 states, Washington, DC, and U.S. territories with the exception of Puerto Rico, which tracks pregnancies in a separate database. The registry began to gather data in January 2016, shortly after the CDC issued its first alert for pregnant women to avoid travel to places where the vector-borne virus was being transmitted locally. The data released Tuesday includes information gathered over the year that followed, through Dec. 27. During that time, the CDC amended its recommendations to reflect findings that the virus also is sexually transmitted. Local transmission of the virus in the United States was not reported until June 2016. The women whose pregnancies were tracked in the just released data were infected through travel, either their own or a male sexual partner’s, to a range of 16 countries or territories: Barbados, Belize, Brazil, Cape Verde, Colombia, Dominican Republic, El Salvador, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, Puerto Rico, Republic of Marshall Islands and Venezuela.
Still the numbers fall far short of presenting even an estimate of the potential rates of risk to infants and fetuses posed by the virus. Subsequent to launching the registry, the CDC recommended neuro-imaging — or brain scans — for all live-born infants from pregnancies with possible Zika infection, for early detection of abnormalities not otherwise immediately evident, including ones leading to developmental impairments, hearing deficits, movement limitations, seizures and inconsolable, incessant crying. But during this first year of the registry, just one in four of the babies born to mothers with confirmed Zika infection during pregnancy received postnatal neuro-imaging.
Rates of birth defects were similar among women who had, and had not experienced symptoms of Zika infection, which in the majority of cases goes unnoticed. Still, authors reporting the data caution that women with symptoms may have been more likely to be tested than women without symptoms, as might women in whom prenatal testing had detected abnormalities, and that miscarried fetuses showing abnormalities may have been more likely to be tested for Zika exposure. In addition, the authors note that information collected on other possible factors associated with birth defects, including genetic causes or exposure to other infections, was limited. At the same time birth defects in stillborn infants or miscarried infants with Zika exposure may not have been reported at the same rates as those for live-born infants.
The data, in an early released CDC Morbidity and Mortality Weekly Report, follows an MMWR released the week before showing rates of the paralyzing Guillain–Barré syndrome rising in parallel to rates of Zika virus infection from May 2015 to December 2015 as the virus spread across 48 countries and territories in the Americas.