U.S. health officials have added two more Caribbean islands to a Zika travel alert for pregnant women.

The Centers for Disease Control and Prevention put Aruba and Bonaire on the list Thursday. There are about 30 destinations with Zika outbreaks, mostly in the Caribbean and Latin America.

The CDC recommends that pregnant woman postpone travel to those places because of a suspected link between the Zika virus and a rare birth defect.

The health agency also advises women who are trying to get pregnant or thinking of getting pregnant to talk to their doctor before traveling to those areas.

The virus, which can cause a mild illness, is spread primarily through mosquito bites.