The CDC provided few details about the women, their pregnancies, birth defects or their severity in its first accounting of pregnancy outcomes involving the virus.

Three babies with birth defects caused by Zika have been born in the US.Birth defects from Zika were also seen in three other pregnancies that ended.

All the cases are connected to travel to areas with outbreaks of the mosquito-borne virus, primarily Latin America and the Caribbean. There has been no local spread of Zika in the US.

Overall, 756 cases of Zika have been reported in the 50 states and Washington DC. All were in people who had traveled to outbreak areas, or had sex with someone who did.

The six cases of birth defects involved some women who had not experienced Zika symptoms. Most people infected never develop symptoms. Others get a fever, rash, joint pain or red eyes, and recover within a week.

The virus is spread mainly through the bite of a tropical mosquito.