1 in 10 Zika pregnancies in U.S. result in birth defects

About one in 10 pregnant womenwith confirmed Zika infections had a fetus or baby with birthdefects, offering the clearest picture yet of the risk of Zikainfection during pregnancy, U.S. researchers said on Tuesday.

The report from the Centers for Disease Control andPrevention is the first to analyze a group of U.S. women withclear, confirmed test results of Zika infection duringpregnancy.

Once considered a mild disease, a large outbreak of thevirus that began in Brazil in 2015 and quickly spread throughthe Americas revealed that the mosquito-borne virus can causesevere brain damage and microcephaly, or small head size, whenwomen are exposed during pregnancy.

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"Zika continues to be a threat to pregnant women across theU.S.," Dr. Anne Schuchat, acting director of the CDC, said in astatement. "With warm weather and a new mosquito seasonapproaching, prevention is crucial to protect the health ofmothers and babies."

Babies affected by Zika can develop congenital Zikasyndrome, which includes brain abnormalities, vision problems,hearing loss, and problems moving limbs.

The study comes from the CDC's Zika pregnancy registry,which includes data from the continental United States and allU.S. territories except Puerto Rico.

The researchers analyzed data on nearly 1,000 completedpregnancies in 2016 among women who had some evidence of Zikainfection. Most were infected through travel to a region wherethe virus was actively spreading.

Of the 1,000, 51 or about 5 per cent had babies or a fetuswith one or more Zika-related birth defect. Because oflimitations of testing, only tests done within the first fewweeks of Zika can test specifically for the Zika virus.

The team also analyzed 250 women with definitive testresults for Zika. Among these, about one in 10 had a fetus orbaby with birth defects. The risk was even higher among womeninfected in the first trimester of pregnancy, where 15 per centof pregnancies resulted in a fetus or baby with birth defects.

The study also showed that three out of four babies exposedto Zika had not received brain imaging after birth to diagnosebirth defects.

"We know that some babies have underlying brain defects thatare otherwise not evident at birth. Because we do not have brainimaging reports for most of the infants, our current data mightsignificantly underestimate the impact of Zika," CDC's PeggyHonein told a news briefing.