Twenty-one weeks into her pregnancy Brook Meakins and her husband started to regret their "babymoon"—a vacation celebrating just the two of them before their burgeoning family grew to three. Right before Christmas they had left for a luxurious trip to Bora Bora that they had planned well in advance. From there they went to Easter Island for another week and then decided to swing back through Bora Bora for a few more days.

But last week their nightmare began. They spent Martin Luther King Day at the emergency room back in California, where doctors gave Meakins a battery of tests for her rash and achy joints. Just days earlier the U.S. Centers for Disease Control and Prevention had issued its first-ever warning for pregnant women and Zika disease—advising expectant mothers to avoid 13 countries and Puerto Rico where the mosquito-borne virus was rapidly spreading. The list of spots to avoid did not include French Polynesia, but Zika has been known to surface there in the past and her doctors had said there was cause for concern. Although Meakins tried to avoid getting bitten—thinking of other mosquito-borne threats because Zika was not even on their radar—she did receive about a dozen bug bites on their trip, particularly in Bora Bora. “I have thought many times these past few days about how none of this would have happened if we had just canceled the trip,” Meakins says.

The CDC is not necessarily concerned with the effect of Zika virus disease on pregnant women like Meakins because its symptoms are relatively mild and could last about a week. Instead, its links to a serious birth defect called microcephaly is what prompted the agency to put out the warning and why Meakins is losing sleep at night. That condition, which results in the fetus developing an abnormally small head, may also include potentially debilitating brain damage. In Brazil, where Zika is increasingly common, there have been more than 3,500 cases of microcephaly—more than 20 times the norm for the country. Doctors still do not know how often pregnant women with Zika go on to have children with microcephaly but they are now on the lookout for it.

Already the Hawaii State Department of Health announced last week that in the state one baby was born with microcephaly to a mother who was likely infected with Zika when she lived in Brazil in May 2015. And yesterday Illinois public health officials confirmed two pregnant women in their state have also tested positive for the virus after one traveled to Honduras and another went to Haiti. The CDC is now steeling itself for more such cases.

At the hospital on MLK Day, Meakins gave a blood sample that will be sent to the CDC for further testing. She says she was told not to expect the results for four to 14 days. The wait, unsurprisingly, is agonizing. “We are balls of worry right now, although we are trying to stay positive, love each other through and stay on top of the research as it comes in,” she says. Their fetus was the product of in vitro fertilization and so “he was a little miracle already,” she says.

Tests for Zika are cumbersome and limited. At the CDC, there are several tests they can do to hunt for signs of the virus. Right after infection there are several days when the virus is in the blood so the CDC could use a method called reverse transcription–polymerase chain reaction to amplify the viral genetic material if it is present and detect it. The window for such testing, however, only lasts about a week. “Once the person is infected and after their immune system kicks in and they start developing antibodies to fight the virus you can’t find it,” says Erin Staples, a medical epidemiologist at the CDC. At that point, the search would focus instead on antibodies that show up due to a recent exposure to the virus. If those antibodies are present, then the CDC would do another confirmatory test—one whose results would take about a week to complete—that involves taking the person’s blood that should contain antibodies and exposing it to the virus in the lab. That final test is necessary because Zika virus closely resembles similar pathogens like dengue and yellow fever, which could lead to false positives, Staples says.

Yet if Meakins does turn out to have had Zika, there are no steps doctors can take to try to prevent transmission of the disease to the baby—or to prevent microcephaly. Despite years of expertise preventing transmission of diseases like HIV to fetuses, there is too little information on Zika to know what would work with this tropical virus. Under certain circumstances with HIV, for example, doctors recommend a C-section delivery to help reduce chances of disease transmission, but there have been so few studies on Zika virus disease that “we don’t have enough information at this point to make any recommendations at this point in that area,” says Denise Jamieson, a medical officer in the CDC's Division of Reproductive Health. The CDC recommends instead that expectant mothers should consult an infectious disease specialist with expertise in pregnancy. And if the fetus does look like it will have microcephaly, to deliver it somewhere with a robust neonatal and obstetric care department.

On January 19 the CDC released guidelines for obstetricians stating that doctors should be sure to ask pregnant women about their recent travel history, and advise them if they had visited locations where there is active Zika transmission to be tested for the virus. The guidelines—which the CDC stresses will evolve with more information—also include instructions for close monitoring of such women with ultrasounds every few weeks and potential testing of amniotic fluid to look for the viral RNA from Zika. With those ultrasounds, “you can see the anatomy of the brain and have some estimate of the severity of the damage to the brain,” Jamieson says.

Regardless of the test results, Meakins’s doctor, David Marinoff, a specialist in high-risk obstetrics at Alta Bates Summit Medical Center in Berkeley, Calif., says he plans to do ultrasounds every four weeks to ensure the pregnancy is progressing smoothly and the baby’s brain is developing normally. “There might be something going on we didn’t test for,” he says, noting they also did tests for other mosquito-borne illnesses that she may have been exposed to in her travels. Moreover, with Zika, “no one knows what the attack rate is—how many women who are pregnant end up with babies who have microcephaly” he says. For the Meakinses, at least for now, there is no thing to do but wait.