Berg Cynthia J, Callaghan William M, Henderson Zsakeba, Syverson Carla
Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, Georgia (Berg, Callaghan, Henderson) Empowered Global Solutions, Englewood, Colorado (Syverson).
Obstet Gynecol. 2011 May 1;117(5):1230. doi: 10.1097/AOG.0b013e31821769ed.