More than 20,000 babies in the U.S. were born with congenital rubella syndrome during an outbreak of rubella in 1964-65. A vaccine developed in 1969 helped curb the virus's spread but hasn't eliminated it worldwide.
Public Health Image Library/CDC
A woman who is six months pregnant shows a photo of her ultrasound at the IMIP hospital in Recife, Pernambuco state, Brazil, on Wednesday. Scientists are trying to figure out how Zika virus may be affecting fetuses.