American mothers infected with the Zika virus last year were 20 times as likely to give birth to babies with birth defects as mothers who gave birth two years before the epidemic, federal health officials said on Thursday.
The Centers for Disease Control and Prevention concluded last April that Zika infection caused severe birth defects, including the abnormally small heads of microcephaly, but it had not previously estimated how common such defects were.
A new study, published in the agency’s Morbidity and Mortality Weekly Report, looked at several hundred pregnant women entered into the C.D.C.’s Zika Pregnancy Registry after lab tests indicated they had probably had the virus. The study compared their birth outcomes to those found in historic registries of birth defects kept in Massachusetts, North Carolina and Georgia.
It found that in 2013 and 2014, those states’ typical rate of severe birth defects — including microcephaly, brain abnormalities, eye defects or central nervous system problems — was about 3 out of every 1,000 live births.