[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, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Med Effectiveness Res Ctr Diverse Populat, San Francisco, CA 94143 USA
[5] Kaiser Permanente, Dept Obstet & Gynecol, San Francisco, CA USA