The mosquito-borne Zika virus may be even more dangerous than previously thought, scientists in Brazil say.
Leading doctors have told the BBC that Zika could be behind more damaging neurological conditions, affecting one in five pregnant women who contract it.
Rates of increase in Zika infection in some parts of Brazil have slowed, thanks to better information about preventing the disease.
But the search for a vaccine is still in the early stages.
And Zika continues to spread across the region.
Most doctors and medical researchers now agree that there is a link between the Zika virus and microcephaly, where babies are born with abnormally small heads because of restricted brain development.
While it is estimated that 1% of women who have had Zika during pregnancy will have a child with microcephaly, doctors in Brazil have told the BBC that as many as 20% of Zika-affected pregnancies will result in a range of other forms of brain damage to the baby in the womb.
A separate study, reported in the New England Journal of Medicine, said that "29% of scans showed abnormalities in babies in the womb, including growth restrictions, in women infected with Zika".
Zika: What are the symptoms?
Deaths are rare and only one in five people infected are thought to develop symptoms.
-conjunctivitis (red, sore eyes)
A rare nervous system disorder, Guillain-Barre syndrome that can cause temporary paralysis has been linked to the infection.
There is no vaccine or drug treatment so patients are advised to rest and drink plenty of fluids.
But the biggest concern is the impact it could have on babies developing in the womb.