NIH and a Brazilian health research agency have launched an international study of almost 10,000 pregnant women in Zika-affected areas. Infection with the Zika virus causes small heads and other neurological birth defects in some children whose mothers contracted the disease while pregnant. But the full scope of how Zika causes these defects is not known. The agencies will recruit women in their first trimester of pregnancy and then follow them and their children for a year after birth. “This large prospective study promises to provide important new data that will help guide the medical and public health responses to the Zika virus epidemic,” says Anthony S. Fauci, director of the National Institute of Allergy & Infectious Diseases, one of the NIH centers supporting the research. The study will start in Puerto Rico and expand to Brazil, Colombia, and other areas where Zika has been transmitted to people by Aedes aegypti mosquitoes. The White House has asked for more funds to support Zika research and response.