Babies in Zika-affected pregnancies in the United States are about 20 times more likely to have birth defects compared with the proportion of pregnancies seen in 2013-2014, before Zika was introduced into the Americas, according to the Centers for Disease Control and Prevention.
The types of birth defects associated with Zika include brain abnormalities and/or microcephaly, neural tube defects and other early brain malformations, eye defects and other central nervous system problems.
Those defects were seen in about three of every 1,000 births in 2013-2014 in the U.S., but in 2016, the proportion of infants with these same types of birth defects born to women with Zika virus infection during pregnancy rose to about 6 percent, or nearly 60 of every 1,000 completed pregnancies with Zika infections, according to a CDC report.
These findings demonstrate the importance of having monitoring systems that collect data on birth defects, as well as why pregnant women and their partners should be educated about them, doctors say.
"There's been such a massive improvement in taking care of these birth defects, that, however terrifying it is, it's important for mothers to get their follow-up appointments and their doctors, and make sure they're delivering in a center where people know how to take care of the defects," says Dr. Tala Nasr, a neonatologist the Pediatrix Group at Medical City Children's Hospital in Dallas.
The CDC researchers analyzed 2013-2014 data from three birth defect surveillance programs in the United States (in Massachusetts, North Carolina and Georgia) to provide the baseline frequency for Zika-related birth defects. To assess the effect of Zika virus infection during pregnancy, the scientists compared that 2013-2014 baseline number with previously published numbers among pregnancies with Zika virus infection from the U.S. Zika Pregnancy Registry (USZPR) from 2016.
They identified 747 infants and fetuses with one or more of these defects from programs in Massachusetts, North Carolina and Georgia from 2013-2014. Brain abnormalities and/or microcephaly were the most frequent conditions reported.
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Data from the USZPR identified 26 infants and fetuses with these same birth defects among the 442 completed pregnancies of women with possible Zika infection from January through September 2016.
Studies have shown that Zika's arrival to Brazil at least doubled the birth defect rate there, even though the mosquito-borne virus only seriously affected small areas, NBC News reported.