[1] Univ Calif San Francisco, Dept Obstet Gynecol & Reprod Sci, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Dept Med, Div Gen Internal Med, San Francisco, CA 94143 USA