The Zika virus may cause microcephaly in unborn children at a rate as high as 13 percent, a new study has found. The condition, which can result from a pregnant mother contracting Zika from an infected mosquito, leads to babies born with abnormally small heads and severe brain damage. Typical rates for microcephaly range from 0.02 to 0.12 percent of all US births. New research, conducted by analyzing data from Brazil and published today in The New England Journal of Medicine, shows a staggering jump in the risk rate if a mother is infected with Zika in the first trimester.

The range of risk spans from 1 percent to 13 percent, the study says, as researchers could not be certain about the overall rate of infection in the population studied and the accuracy of microcephaly diagnoses. There was "a negligible association in the second and third trimesters," the authors write. At the moment, the research is restricted to Brazil, and no other country with local Zika transmissions has exhibited the increase in microcephaly rates. However, as Zika continues to spread, the situation in Brazil may be replicated elsewhere.