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LAS VEGAS -- Ob/gyns and their patients now know much more about the Zika virus than they did a year ago, but expectant mothers still need to be cautious, an expert said.

In a special session at the Society for Maternal-Fetal Medicine (SMFM) annual meeting, , of Massachusetts General Hospital (MGH) in Boston, noted the recent statistics from the U.S. Zika Pregnancy Registry, which estimated a 11% rate of birth defects associated with mothers who reported symptoms or exposure in the first trimester.

She added that for U.S. women who have reported exposure and infection in the second or third trimester, there have been no confirmed birth defects yet.

"We're still going to need to be cautious before we say there are no problems," said Riley, noting that some effects of Zika can manifest months after birth.

The session also emphasized the importance of ob/gyns and pediatricians working together, as pediatricians are now starting to see the impact of Zika-affected infants. Riley gave the example of a patient who found out they were exposed to Zika, but was outside the 12-week window for testing.

"Not only should you do the ultrasound and have the conversation that the patient may be at risk, but inform the patient's pediatrician," she said. "The CDC has noticed that communication to the pediatrician is often forgotten in the process."

Riley also said that the pediatric guidelines for Zika testing may change "very soon," so ob/gyns should be on alert.

Riley discussed the potential for new testing and eventually, a vaccine. "Every 2 weeks, when we have a call with the CDC, Phil Heine asks 'Where's the IgG test?'" said Riley. "We want to be able to say to people 1 to 2 years down the road, 'You've had this, let's move on.'"

, of Duke University in Durham, N.C, along with Riley and and , also of MGH, developed the from SMFM and the American College of Obstetricians and Gynecologists.

One SMFM attendee noted that the IgG test has been used in Europe, but interpreting the results has been difficult.

The CDC has mentioned 2018 for their first IgG test, but Riley emphasized the organization "needs confidence in the results, so the FDA does not want to use it yet."

Placental Trophoblasts

An reported that the virus replicated in placental trophoblasts, which supply the embryo with nourishment and help form part of the placenta. The findings were published simultaneously in

, of Baylor College of Medicine in Houston, and colleagues isolated Zika virus from an infected patient from Colombia, and infected placentas from 20 donors who had already delivered infants who were not exposed to Zika. They exposed the uninfected placentas to Zika virus for 1 hour, and found that 8 days later, Zika cells were continuing to replicate in these trophoblasts, and did not kill them.

"[This] was important in not only establishing a potential portal for Zika virus transmission from mother to fetus, but in helping us understand why some pregnant women continue to have detectable virus in their blood or urine for many, many months after initial infection," said Aagaard in a statement.

The researchers attempted their experiment with dengue virus, but did not find the same results. They concluded that Zika has a different mechanism of action that allows it to continue to replicate in placental trophoblasts.

Zika in Colombia

A used fetal ultrasound and MRI to examine infants from Colombia who were born with Zika virus. , also of Baylor, and colleagues found that there was a significant association between microcephaly, brain calcifications, and fetal neurological abnormalities, such as ventriculogmegaly, in infants with congenital Zika virus infection.

This was the first study to examine fetal brain imaging from Zika in Colombia, according to the authors. They looked at 214 pregnant patients with suspected Zika virus exposure using fetal MRI.

Overall, 13 cases presented with brain abnormalities (11 confirmed, two presumed). They found that microcephaly was the most common finding, but did not occur in all cases, and warned it should "not be considered a screening method to detect fetuses with Zika." There were cortical abnormalities in 80% of infants with Zika.

Researchers also found that there was significantly increased ventricular volume, and decreased supratentorial brain parenchyma in infants infected with Zika.

They concluded these numbers were similar to Brazilian cohorts, meaning the infection has followed a similar pattern in both countries.