Pregnant U.S. women infected with the Zika virus were 20 times more likely to have babies with certain birth defects, compared with the prevalence of those birth defects before the Zika epidemic reached the United States, according to a CDC report released Thursday.
According to the Washington Post's "To Your Health," providers say the findings highlight the importance of early and accurate Zika testing for pregnant women.
The study, published in CDC's Morbidity and Mortality Weekly Report, examined birth outcomes for hundreds of women entered into the agency's Zika Pregnancy Registry last year after tests indicated they likely had the virus. The researchers compared the women's 2016 outcomes with birth defect data from 2013 and 2014—before the Zika epidemic came to the United States—recorded in registries kept in Georgia, Massachusetts, and North Carolina.
The researchers found that in 2013 and 2014, the rate of the kinds of birth defects typically associated with Zika—including microcephaly, brain abnormalities, eye defects, or central nervous system problems—was 2.86 per 1,000 live births.
In comparison, the researchers identified 26 infants and fetuses with the same birth defects among 442 pregnant women who were infected with Zika during a nine-month period in 2016. CDC said that figure equates to a rate of 58.8 per 1,000 pregnancy outcomes. According to the report, 22 of the 26 infants and fetuses had a brain abnormality or microcephaly—a rate about 33 times higher than the prevalence among infants born before the epidemic.
Janet Cragan, a medical officer at CDC's birth defects branch who led the research, said the findings provide "an idea of how large the risk may be."
It is still too early to estimate with certainty how a Zika diagnosis affects the risk of birth defects, according to Margaret Honein, chief of the CDC's birth defects branch who worked on the study. She noted that comparing the rate of live births to a rate based on all pregnancy outcomes "is not a perfect comparison. But the difference between three times per thousand and 60 times per thousand does give you the magnitude of the increase" (McNeil, New York Times, 3/2; Sun, "To Your Health," Washington Post, 3/2; Healy, "Science Now," Los Angeles Times, 3/2).
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