The county is the only area in the continental U.S. where mosquitoes have been continuously spreading the virus since the summer. The test is recommended for pregnant women who lived in -- or visited -- Miami-Dade since August 1, whether or not they have symptoms.
The Centers for Disease Control and Prevention sent out the advisory Wednesday.
Zika is mainly spread by mosquitoes. Infection during pregnancy can lead to severe brain-related birth defects.