In 2013 and 2014, three programs tracking birth defects — in Massachusetts, North Carolina and metropolitan Atlanta — recorded 747 infants and fetuses with microcephaly and or other abnormalities of the central nervous system and eyes — about three in every 1,000 births.
That was during what the U.S. Centers for Disease Control and Prevention now calls “the pre-Zika years,” before 2015 when the virus that has since been confirmed to be a cause of those birth defects in children born to mothers infected during pregnancy landed in the Western hemisphere and began to be spread here by local mosquitoes, travel and sexual transmission.
The rate of those defects now is an estimated 20 times higher in infants and fetuses apparently exposed to the virus, or about 60 in every 1,000 births, according to researchers who compared the pre-Zika data from the three programs to data from the U.S. Zika Pregnancy Registry created in 2016 to track the outcomes of pregnancies among women in the U.S. whose laboratory tests showed evidence of possible Zika infection. The conclusion was based on findings in 26 infants and fetuses among 442 completed pregnancies.
The findings are subject to some limitations, according to the researchers, whose conclusions are in the CDC Morbidity and Mortality Weekly Report released today, including that pregnancies with prenatally detected abnormalities may be likelier to have led to testing for the virus, and then be included in the registry, that some pregnancies in the “pre-Zika” years may have been affected by travel related and sexually transmitted infections of the virus, and the greater possibility that some relevant birth defects could have been missed in the earlier programs than in the Zika registry.
Still, the researcher say, their findings add to a growing body of data on Zika related impacts, and their ability to gather the findings underscore the importance of population-based surveillance of birth defect incidence, an effort that will grow under funding CDC has provided to 45 local, state and territorial health departments to track birth defects related to Zika.