As many as 10,000 pregnant women could participate in a massive new international study of the Zika virus, announced Tuesday by the National Institutes of Health.

NIH is working with Fiocruz, a research organization linked to the Brazilian Ministry of Health, to evaluate the severity of health risks the Zika virus poses to pregnant women and their developing fetuses and infants. Researchers plan to track participants through their pregnancies, observing whether they become infected with the virus and if so, the health complications they incur.