The Centers for Disease Control and Prevention recently reported that nine pregnant women were known to have become infected while traveling. Yet many more are coping with the possibility of exposure, reaching out to their doctors for blood tests and ultrasounds, obsessing on news coverage and trying to manage their worry.
The C.D.C. recommends that pregnant women receive blood tests two to 12 weeks after travel to an affected area to detect whether they may have been infected with the Zika virus.
Those who may have been exposed are urged to consider having extra ultrasounds to look for birth defects in the developing fetus.
Nothing is guaranteed; the antibody test has its limits. Ultrasounds often do not detect fetal microcephaly, the disease causing misshapen heads and brain damage that has been linked to infection with the virus.
According to the C.D.C., the scans are most accurate at the end of the second trimester or early in the third.
“The risk is small, but the effects are tragic,” said Craig Forest, 37, an associate professor of bioengineering at Georgia Tech in Atlanta.
He and his wife, Roxanne, 32, spent Christmas vacation in Costa Rica just as she was entering her second trimester of pregnancy.
They chose that destination because of all the countries in the region, it seemed to offer the safest environment for a pregnant woman.
After 10 days of rain forest hikes and lazy sunsets on the beach, Ms. Forest was covered with insect bites.
Back home in January, the couple began hearing news reports about the Zika virus. Costa Rica was not mentioned.
“I’m looking at the list and thinking, ‘That’s all of Costa Rica’s neighbors; we dodged a bullet on that one,’ ” Mr. Forest said.
On Feb. 1, Costa Rica was added to the list of countries in which Zika is circulating. The virus had been in the country since at least December.
Ms. Forest’s doctor did not order a blood test for the infection, because she had not had any symptoms. Her most recent ultrasound appeared normal, and the couple say they will ask for another at the cutoff time for an abortion.
They have lain in bed at night discussing the possibility, something that would have been unthinkable a couple of months ago.
They know the risks are remote — first that she might have been bitten by an infected mosquito, and second that the infection might lead to a birth defect.
“As analytically minded people, we’re trying to calculate the odds,” said Ms. Forest, who is also an engineer.
But when they try to figure the likelihood of a birth defect related to the Zika virus, all they can come up with is “not zero.”
There is nothing to do but wait. “I actually tried to stop reading the news,” Ms. Forest said.
Even when a pregnant woman is found to have been infected, tests of blood or amniotic fluid cannot definitively tell if the fetus was affected, said Dr. W. Ian Lipkin, an expert in infectious diseases at Columbia University’s Mailman School of Public Health, who is working to develop a more reliable alternative.
Microcephaly seems to be a relatively rare complication. But it’s also possible that the virus may cause “more subtle damage that we can’t yet appreciate,” Dr. Lipkin said.
Sydney Silverstein, 35, an Emory University doctoral candidate, has been living in Iquitos, Peru, since July. She is eight and a half months pregnant.
There is no widespread epidemic of Zika virus in Peru, but the virus is present in Lima. Moreover, she spent time on the Brazilian border in late fall, early in her pregnancy.
She has had extra ultrasound scans from her doctor, and her fetus looks unaffected.
Her husband, Nick, travels back and forth from his job in Ohio, and her parents have been urging her to leave before the virus spreads to her part of the country. “I have a family that is awesome and supportive — and a little freaked out,” she said.
Ms. Silverstein decided to remain in Peru, believing the risks to her baby boy are not great and wanting to complete the research she has started.
Still, the difference between her circumstances as an American and those of other local women “smacks you in the face,” she said.
“Deep down, I knew I had the option to leave if I thought I had to.” Most women in Latin America cannot.
In late February, just after Ami Levy first heard her baby’s heartbeat in the doctor’s office, her Zika antibody test results came back negative. “For the first time in weeks, I felt like I could breathe,” she said.
She had spent an anxious month worrying that she had put her baby in danger, though she knew the guilt to be illogical. Even now, Ms. Levy says she is nagged by the knowledge that the tests are not foolproof. She plans to ask for an extra ultrasound when she is further along.
She’s taking no chances, even tiny ones. At her doctor’s suggestion, she canceled a coming trip to Florida because the local health authorities had declared a public health emergency in Miami-Dade County.
“I see those pictures, and I feel connected to those mothers in Brazil,” she said. “This is a really horrible situation.”
Correction: March 16, 2016
A picture caption on Tuesday with an article about a woman who has been monitoring her pregnancy because of possible exposure to the Zika virus misspelled her surname. She is Ami Levy, not Levi.