[1] UCSF, Dept Family & Community Med, 1001 Potrero Ave, San Francisco, CA 94110 USA
[2] UCSF, Dept Obstet Gynecol & Reprod Sci, 1001 Potrero Ave, San Francisco, CA 94110 USA
[3] UCSF, Dept Epidemiol & Biostat, 1001 Potrero Ave, San Francisco, CA 94110 USA
[4] Kaiser Permanente Northern Calif, Div Res, 2000 Broadway, Oakland, CA 94612 USA