A total of 508 confirmed cases of microcephaly have been reported in Brazil. The figure indicates a 10% rise in less than a week, said the Health Ministry. Microcephaly is a serious birth defect suspected of being linked to the Zika virus.
The latest figure was up from 462 confirmed cases on February 12, 2016, the health ministry said.
Another 3,935 suspected cases of microcephaly, in which a baby is born with an abnormally small head and often incomplete brain development, are being investigated.
Scientists in Brazil say the increase in microcephaly is linked to an explosion of the mosquito-transmitted Zika virus, with an estimated 1.5 million people infected.
The virus usually causes mild flu-like symptoms, but scientists say it might cause microcephaly in the fetuses of women infected while pregnant.
The World Health Organization is studying the possible link and calls the Zika outbreak an international health emergency.
In the absence of a vaccine against Zika, Brazil is mounting a huge operation to eradicate the mosquito responsible for carrying the virus.
Tens of thousands of troops have been called up to help health workers educate the public and eliminate pools of stagnant water where mosquitoes breed.
"The mosquito is completely domestic. It can be born, grow and live inside houses," health worker Paulo Lopez said as he fumigated residences in a suburb of the capital Brasilia on February 17.
With less than six months to go before the Olympic Games kick off in Rio, Brazil is under pressure to reassure international travelers and athletes that they run no risk from the little-understood virus.