The chances of delivering a baby with a birth defect are about one in 16 for mothers infected with Zika while pregnant, according to a new report published in the Journal of the American Medical Association using preliminary data from the U.S. Zika Pregnancy Registry.
The report combined data from the continental United States and Hawaii that were collected by the Centers for Disease Control and Prevention and state and local health departments. The health agencies are monitoring pregnancies with evidence of Zika.
Of the 442 U.S. women with possible Zika virus infection, 26 — or 6 percent of the women — reportedly had children with birth defects possibly related to the Zika infection. These women were exposed to the virus while pregnant in Barbados, Belize, Brazil, Colombia, Dominican Republic, El Salvador, Guatemala, Haiti, Honduras, Mexico, Republic of Marshall Islands and Venezuela. In Florida, 193 pregnant women have lab evidence of Zika, according to the Florida Department of Health.
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Among women infected with Zika in the first trimester of pregnancy, 11 percent were reported to have fetuses or infants with birth defects, which is consistent with previous modeling estimates. The proportion of pregnancies with birth defects was similar for pregnant women who did or who did not experience symptoms, about 6 percent in each group.
“This is an important study. It shows that the rate of microcephaly and other fetal malformations related to Zika is similar among babies born in the United States — whose mothers were infected during travel to a dozen countries with active Zika transmission — to the estimated rate in Brazil,” said CDC Director Dr. Tom Frieden. “Zika poses a real risk throughout pregnancy, but especially in the first trimester; it’s critical that pregnant women not travel to areas where Zika is spreading.”
The 18 infants with microcephaly represent 4 percent (18/442) of the completed pregnancies; this prevalence is substantially higher than the rate of microcephaly cases in the United States of about 7 per 10,000 live births, or about 0.07 percent of live births.
A recent report of infants in Brazil with congenital Zika virus infection documents how an infant can appear healthy at birth but later experience slowed head growth and microcephaly. Given these recent findings from Brazil, it is possible that a greater proportion of the infants in the CDC report could be affected by a Zika-related birth defect within the first year of life.
The CDC urges pregnant women to avoid areas with Zika. For more information about the Zika virus and pregnancy, visit the CDC website.