With warmer weather approaching, the Zika virus is again making headlines. This time, U.S. health officials are warning that pregnant women who have Zika are 20 times more likely to have a child with birth defects than pregnant women who don’t have the virus.
Margaret Honein, chief of the birth defects branch at the CDC, says that “when you look just at brain abnormalities and microcephaly, what we are seeing is more than 30 times higher than the prevalence before Zika was introduced to the Americas.” 
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Microcephaly causes babies to be born with smaller-than-normal heads, along with an underdeveloped brain. Thousands of babies have been born with the Zika-linked birth defect since Zika began to spread throughout South American in April 2015. The virus exploded so rapidly in Brazil last year that the World Health Organization (WHO) declared a Public Health Emergency of International Concern. The link between the Zika virus and microcephaly is confirmed, but it was still questionable at the time. 
“I think women should take that this further demonstrates how important it is to prevent Zika virus infection during pregnancy. These devastating effects have a major increase over the baseline when Zika virus infection occurs during pregnancy.”
Assessing the Danger
For the study, published in the CDC’s journal, Morbidity and Mortality Weekly Report, researchers looked at data on several hundred women from the CDC’s Zika Pregnancy Registry after tests revealed the women probably had the virus. The team compared their birth outcomes to those found in historic registries of birth defects kept in Massachusetts, North Carolina, and Georgia. 
They found that, in 2013-2014, the typical rate of severe birth defects, including microcephaly, brain abnormalities, eye defects, or central nervous system problems, accounted for about 3 in 1,000 births in those states.
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However, the 442 women in the pregnancy registry had 26 infants and fetuses with similar defects, which increased the rate to about 60 out of every 1,000 pregnancy outcomes, including live births, miscarriages, and abortions.
While those numbers aren’t exact, not every American woman who had Zika is being followed in the pregnancy registry. Still, Honein says “the difference between 3 times per 1,000 and 60 times per 1,000 does give you the magnitude of the increase.”
About 300 women in Washington, D.C. are currently being retested for Zika. Lab workers there reportedly misread labels and watered down test solution that was already diluted, producing false negative results. Federal officials say the problem is not believed to have occurred at any other state or city laboratory.