Two years ago, when the Zika virus was first identified as the cause of microcephaly in babies, women were scared. Expectant mothers who got infected had no idea what the chances were of having a healthy baby.
Researchers have since learned that while Zika infection is dangerous, about 94 percent of babies born to women infected with Zika appear to be normal at birth.
Yariel is one of them. He's a curious little 1-year-old — calm and smiley, with a head full of curls. Looking at him, it's impossible to know that his mother had Zika when she was pregnant.
Yariel is a patient of Dr. Sarah Mulkey, a fetal neonatal neurologist at Children's National Health System in Washington, D.C., who is studying babies born to women with Zika to try and find out how OK they really are.
At Yariel's one-year checkup, Mulkey measured his head and checked his reflexes. She knelt on the floor of the exam room with him, observing how he moved from sitting to crawling and back, how he rolled over. A favorite stuffed Mickey Mouse toy served as enticement.
To get Yariel to pull up to standing required some extra encouragement.
"Come here! Let's go," his mom, Yaritza Martinez coaxed, tapping the chair next to her. And he does.
"He stood up on his own — good," Mulkey said, marking her sheet. She went through a lengthy questionnaire for her research: Can he drink from a cup without a lid? (Not yet.) Does he sing along to familiar songs? (All the time.)
"Everything as far as his development looks normal today," Mulkey told Martinez. "His exam looks great."
A Nerve-Wracking Pregnancy
Last spring, Martinez had no idea that this is how her story would turn out.
When she was 12 weeks pregnant, she flew from her home in Takoma Park, Md., to the Dominican Republic to take her mom to an immigration appointment. Zika has been a big risk there, and when she got back, she felt sick.
"I feel like a fever, and the next day, I saw the rash on all my body," she said. "They do the blood work, and they say, 'You are positive.'
"I was scared. Really really really scared."
She had good reason to be scared. When Zika infection happens early in a pregnancy, the risks of significant birth defects — including microcephaly, seizures and hearing problems — are greatest.
She was referred to the Congenital Zika Program at Children's, which is a regional hub for Zika treatment. Martinez was put into a study that monitored her baby's brain as it developed using MRIs of her pregnant belly.
"I don't like [it]," she recalled. "It was my first time with MRI — my husband, he took my hand and tried to distract me."
The current recommendation for Zika is to use monthly ultrasounds to monitor the fetal brain, but researchers at Children's have found MRIs give more clarity and sometimes find problems that ultrasounds miss.
She told her doctors to not hold anything back.
"I said, be honest with me. If my baby come with any effect, let me know," she said.
But her doctors didn't find anything worrisome in his scans. "Every time, they check his brain," Martinez recalled. "And they say, 'You see, everything comes normal.' "
Could More Problems Come Later?
That was encouraging, but there was still reason to be nervous. With some l infections during pregnancy, like cytomegalovirus, a baby's hearing could be normal at birth and at a year, but they develop deafness by the time they reach school age.
Dr. Roberta DeBiasi, the director of the Zika program at Children's, says that if a baby makes it through the first year without microcephaly, it's unlikely that any serious brain issues will show up.
"There have been reports of babies that have a normal heads size at birth, but then as they're followed for a year, they develop microcephaly," she said. "But most of those children, if you go back and look at their prenatal ultrasounds, there actually was a hint that the brain wasn't actually growing on the normal curve."
And so far, it seems like hearing loss isn't likely to crop up later with Zika like it does with cytomegalovirus.
"What we don't know is, will they have more subtle things?" DeBiasi said. "Is there autism? Are there learning disabilities or subtle hearing things? That we have to wait and find out."
Mulkey's study, which includes Yariel, is following a group of babies in the U.S. and in Colombia, where Zika is much more prevalent, through their first year.
Those who seem normal at birth are so far on track developmentally.
"Fingers crossed they stay normal. I anticipate they will," she said. "It's good news out of the whole Zika story."
Mulkey would like to take her study even further.
"With anything with babies you don't really know if they turn out OK until you get to school age," she said. "My goal for this would be to follow them to age seven or eight to really know if they're doing OK."
The next step for Yariel is his first birthday party. Yaritza Martinez is planning for a small cake, some family.
Mulkey hopes that she can follow Yariel for many birthdays to come — at least until he goes to school and she can be sure he's really OK.
Selena Simmons-Duffin is a producer at NPR's All Things Considered, currently on a three-month staff exchange with Washington, D.C., member station WAMU, where she is reporting on health.