The Centers for Disease Control and Prevention (CDC) is urging physicians to be more aggressive in screening pregnant women for the Zika virus. The new guidance comes amid growing concerns about Zika, which, if contracted by pregnant women, can result in severe birth defects — including microcephaly, which stunts children’s brain development. It has also been implicated in miscarriages and diseases like Guillain-Barre, a neurological disorder that causes temporary paralysis.

The CDC update recommends that all pregnant women in the United States and its territories should be “assessed for possible Zika virus exposure” whenever they get a prenatal care visit.

Physicians are also being urged to test for the virus if a pregnant woman or her sexual partner have traveled to an area where the virus was actively spreading. Previously, Zika testing was only recommended if they were also showing symptoms — CDC is now recommending testing even in the absence of symptoms.

Zika has been spreading in many Latin American and South American countries, along with Puerto Rico. Public health experts warn it could reach the continental United States by summer’s end. Epidemiologists are investigating two cases in Florida in which local mosquitoes may have transmitted the virus.

Another key part of the new CDC guidelines emphasizes that both symptomatic and asymptomatic pregnant women should be screened within two weeks of the date of possible Zika exposure with PCR, a DNA-based test.

If the PCR test is negative, or an at-risk pregnant woman misses that initial two-week window, the CDC calls for screening with a test that searches for antibodies to the virus. That test, which is effective for as long as 12 weeks after exposure, is considered a less reliable indicator and has drawn some criticism because it can generate false positives.

Click here to read the CDC guidelines.