Goldberg A B, Greenberg M B, Darney P D
Department of Obstetrics, Gynecology, and Reproductive Sciences, Center for Reproductive Health Research and Policy, San Francisco General Hospital and the Univeristy of California, 94110, USA.
N Engl J Med. 2001 Jan 4;344(1):38-47. doi: 10.1056/NEJM200101043440107.