Keila Atuesta Jaimes, a petite 25-year-old, is lying on an exam table next to an ultrasound machine. The doctor moves the wand across her belly. It's pretty flat. She's only about three months pregnant. Then suddenly, there's the heartbeat!

Atuesta smiles. Nervously. About three weeks ago she came down with the kind of rash and fever she figured could mean only one thing: Zika.

She says she went straight to the hospital, concerned her baby might end up with the birth defects that have been linked to Zika: brain damage and an abnormally small head, a condition called microcephaly.

The hospital, in a city called Cucuta, is waiting on a blood test to confirm Zika, but they went ahead and scheduled this special, high-resolution ultrasound. Now Dr. Samuel Bautista, a specialist in high-risk pregnancies, is carefully scanning the image on his screen. It's not enough to measure the head, he says. If this fetus has microcephaly, "I might see little bright spots inside the skull — signs of calcification, signs of damage."

Happily there are none.

"Your baby looks completely normal. There's no problem, OK?" he tells Atuesta.

All the same, he adds, this test was just done to establish a baseline measurement. The key moment won't come until the second or third trimester. That's when they would expect any signs of brain damage to show up.

"You'll need to come back for another ultrasound every month until the baby is born," Bautista explains.

It's a new protocol that Colombia's government has set up to track the progress of every pregnant woman suspected of contracting Zika here — more than 6,300 so far.

Effectively, all these woman have become unwilling participants in a giant science experiment. Since Zika began spreading through Latin America over the past year, hundreds of babies have been born with unusually small heads. But only in Brazil. All eyes are now on Colombia. It has about 37,000 reported Zika cases. And researchers say if there really is a link, Colombia is where the next surge in birth defects could be.

"Suddenly we've found ourselves in the eye of the hurricane," says Fernando Ruiz, Colombia's vice minister of health.

Experts from all over the world are converging on the country, including specialists from the U.S. Centers for Disease Control and Prevention, the Pan American Health Organization and major research universities. They're coordinating with Colombia's own scientists to set up studies.

The first recorded cases of Zika started showing up in October. Ruiz says, based on how things played out in Brazil, that means you'd expect to see the first births of kids with microcephaly here in April — with the largest rush in August. But he adds that there's a glimmer of hope.

"You'd still expect that by now we would have at least had some cases — even just a few cases — of babies born with microcephaly or of signs of birth defects showing up on the ultrasounds."

So far there've been none.

Researchers are still hammering out the details of all the studies they are planning. Peggy Honein, who's completed a scouting trip to Colombia for the CDC, says the health agency will essentially focus on two areas of inquiry.

The first is epidemiology — mapping the Zika spikes to see if they overlap with any surge in the number of birth defects. The other is pathology — checking to see if the virus is present in the tissue and fluids of babies and fetuses.

"The combination of epidemiologic data and pathologic data are both very important," says Honein.

And there are other questions.

"We're also really seeking to gather more information on what the role of timing of infection in pregnancy might be," she says.

In other words, is Zika like rubella, which only affects a baby if the mother is infected very early in her pregnancy?

Doctors here say they can't get the answers soon enough.

Abortion is legal in some cases in Colombia. At a private clinic not far from the hospital, Dr. Orlando Villamizar says he's been having a lot of tough conversations with terrified women who are in their first trimester and have come down with Zika.

"They're saying to me, terminate my pregnancy, because I don't want to have a baby with microcephaly."

It puts him in a tight spot. Even if an ultrasound looks great, he can't guarantee that the baby is fine.

On the other hand, he notes: "I can't say for sure that any of their babies will actually get microcephaly. We could be terminating a pregnancy that is healthy."

For now, he's recommending that his patients keep their babies, and he says all of them have followed that advice.

But basically, he's just waiting for the results of all these studies that are being done on Colombia's women. "All we can do is wait," he says, "and see what happens to them."

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