Zika virus: Agonising wait for pregnant women
In Brazil, there have been around 4,000 reported cases of microcephaly since October 2015.
The infection affects the development of babies' brains and has been linked to the mosquito-borne virus Zika.
The World Health Organisation has said more research is needed to understand the ties between the two.
David Shukman reports from Recife in Brazil, the city worst hit by the outbreak.