WASHINGTON — The number of women infected with the Zika virus during their pregnancies in the continental United States has risen to 234, health officials said on Thursday.
Officials from the Centers for Disease Control and Prevention declined to say how many of the women had given birth, citing confidentiality concerns for the women and their families. But they did cite six cases with abnormalities — three babies with birth defects and another three who died before birth with evidence of defects.
The numbers raised more questions than answers. Without knowing the total number of births, officials cannot know if the babies with birth defects represent a tiny fraction of the total, or a large part. The agency said some of the defects were related to microcephaly, a condition linked to Zika that causes brain damage and abnormally small heads. Others, like eye problems, were Zika-related, but not caused by microcephaly.
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Dr. Denise J. Jamieson, one of the leaders of the pregnancy and birth defects team, which is part of the C.D.C.’s Zika response effort, said the release of the numbers was the first in what will be weekly updates on birth outcomes in Zika pregnancies. As the number of births rises, she said, the agency will be able to release more detailed information.
“We’re sort of in a hard place,” Dr. Jamieson said. “We can’t provide a lot of information about where these women are in their pregnancy. We don’t want to inadvertently disclose information about difficult decisions these women are making about their pregnancies.”
She said the numbers included the nine pregnant women the C.D.C. had reported on in February. Of the babies in those cases, at least one was born with microcephaly.
The C.D.C. also reported on Thursday that the total number of pregnant women who had been infected with Zika in United States territories, including Puerto Rico and the Virgin Islands, was 189. But the agency did not report birth outcomes for that group.
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“Microcephalic babies are beginning to be born,” Dr. Jamieson said. “The disease seems to be very similar no matter where it is.”
Dr. Jamieson said some of the microcephalic births they were seeing were among women who had no symptoms of Zika, a troubling pattern. Roughly 80 percent of people who contract the virus never display symptoms.
She estimated that the approximate risk of having a baby with birth defects — based on findings from Brazil, Colombia and other countries, including the United States — was between 1 percent and 15 percent.
A study published Wednesday in The New England Journal of Medicine found no cases of microcephaly among infants born to women in Colombia who were infected in the third trimester of pregnancy.
“The pattern we are seeing in other places is the same as in U.S. travelers — that Zika is causing birth defects is real,” she said. “It’s not confined to one location or one time period.”
A version of this article appears in print on June 17, 2016, on page A3 of the New York edition with the headline: C.D.C. Finds Over 200 Pregnant Women With Zika in U.S. Order Reprints| Today’s Paper|Subscribe