In a new report from the Centers for Disease Control and Prevention (CDC), researchers compare the rate of birth defects that occurred before the outbreak to the rates that occurred after steps were taken to prevent potential complications linked to the virus. Of the infected women who completed their pregnancies, 6% experienced defects — a clip that’s 20 times what was seen in pregnancies before the epidemic began.

Microcephaly, a condition in which a baby’s head is abnormally smaller due to issues affecting brain development, was the most commonly observed defect. Other defects include problems with the eyes and central nervous system.

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The new figures come in the closing months of winter, a time when the mosquito pool that propagates Zika will begin growing again. Public health officials have urged pregnant women to stay away from Zika-afflicted regions.

One area that officials will undoubtedly keep a close eye on is Florida, as well as certain states along the Gulf coast. These areas have reported local transmission of the Zika virus, with 215 cases in Florida and six in Texas. The CDC declared Florida Zika-free in December, but the agency still advises women to proceed with caution.

Women who are pregnant or trying to become pregnant are urged not to visit countries or territories where Zika virus is prevalent, including Brazil, Puerto Rico, and Southeast Asia where the virus is endemic. Both men and women who have recently been in regions with the virus are strongly encourage to practice safe sex, as it can be transmitted via semen.