MIAMI — Underscoring the serious risk of birth defects from Zika, federal health officials Tuesday reported that about one in 10 pregnant women with a confirmed infection in 2016 had a fetus or baby with a brain abnormality or other neurological disorder associated with the virus.

The risk for birth defects was even higher, about 15 percent, among mothers infected during the first trimester of pregnancy, according to the Centers for Disease Control and Prevention’s latest “Vital Signs” report.

“Zika continues to be a threat to pregnant women in the United States,” said CDC Acting Director Anne Schuchat in a conference call with reporters Tuesday. “With warm weather, a new mosquito season and summer travel rapidly approaching, prevention is crucial to protect the health of mothers and babies.”

The CDC report is the first to analyze a group of pregnant women in the continental United States with confirmed infection reported to the U.S. Zika Pregnancy Registry from Jan. 15 to Dec. 27, 2016.

During that time, 1,297 pregnant women in 44 states were reported to the registry, but only 972 completed their pregnancies, live births and stillborn, in the time frame analyzed.

Among the 972 completed pregnancies, Zika-related birth defects were reported in 51, or 5 percent. But the proportion of birth defects was higher, about 10 percent, when limited to pregnancies with laboratory-confirmed infections.

The distinction underscores the complexity of Zika testing. There is only a narrow time frame, about two weeks after symptoms begin, to obtain a positive lab result that detects the virus molecules in the blood or urine.

After that time, Zika tests can only detect antibodies developed by the immune system to fight the virus — but those tests cannot clearly distinguish between Zika and related pathogens, such as dengue and chikungunya, and they require further testing.

In addition, most people infected with Zika, about four out of five, do not have symptoms, which can include fever, muscle pain, rash and red eyes.

For that reason, the CDC is monitoring all pregnant women with any evidence of recent Zika infection. Schuchat said the Zika pregnancy registry is growing fast.

“We’re still seeing about 30 to 40 new Zika cases in pregnant women each week in the Untied States,” she said.

Schuchat said the CDC will not report individual state results from the national Zika pregnancy registry out of concern for patient privacy. But she added that most of the women included in Tuesday’s report acquired Zika while traveling to an area where Zika was actively spreading in 2016, which includes Miami-Dade.

However, the CDC analysis does not include data from pregnant women in Puerto Rico, where more than 37,000 cases have been reported since 2015, because the U.S. territorial island has its own Zika pregnancy registry.

Birth defects potentially associated with Zika during pregnancy included brain abnormalities, such as microcephaly, eye disorders, central nervous system dysfunction and other neurological problems.

Peggy Honein, co-lead for the CDC Zika Response Team’s Pregnancy and Birth Defects Task Force, said the numbers show an undeniable increase in microcephaly and related neurological defects have increased due to Zika.

The rate of 10 percent reported in 2016 is more than 30 times higher than the baseline prevalence before 2016, which was about three of every 1,000 live births.

“Prevention is key,” Honein said. “There are basic steps people, and especially pregnant women and their male partners, can take to help protect themselves from Zika.”

CDC guidance advises pregnant women to stay away from any areas with risk of Zika, including Miami-Dade, where state health officials in 2016 identified areas with active spread of the virus. In addition, a number of cases were reported in Miami-Dade in 2016 with no identified area of exposure.

In addition, the CDC reported in March that the threat of Zika was even greater for South Florida than previously understood — with a heightened risk since June 2016 for residents in Broward and Palm Beach counties because of local travel patterns and challenges in identifying all areas where the virus was spreading.

Florida health officials confirmed 1,440 Zika infections in 2016, including 292 pregnant women. This year, the health department has reported 34 Zika infections statewide, including 18 pregnant women.

Scientists have known Zika infection during pregnancy can cause microcephaly and other brain abnormalities in developing fetuses. It also can lead to congenital Zika syndrome, which is a pattern of birth defects that includes brain abnormalities, vision problems, hearing loss, and limb defects.

Zika has been nearly dormant in Miami-Dade so far in 2017, with two locally acquired cases confirmed and no zones of active transmission identified.

Florida Gov. Rick Scott’s budget proposal calls for new funding for the health department to hire more scientists and conduct more research to combat the spread of Zika, and Philip said in March that state’s the bureau of public labs has “increased capacity greatly” for testing.

She said by mid-April, the state will begin conducting a complex test for distinguishing Zika from related viruses, such as dengue and chikungunya, that previously only the CDC could perform. Philip said having the state conduct the test, known as a plaque reduction neutralization test, will cut wait times from two to three months to several weeks.

Last year, a backlog of Zika test results led to hundreds of patients, most of them pregnant women, waiting months to receive their results.