[1] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Dept Pediat, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Dept Obstet & Gynecol, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Inst Hlth Policy Studies, San Francisco, CA 94143 USA
[5] Univ Calif San Francisco, Clin & Translat Sci Inst, San Francisco, CA 94143 USA
[6] Kaiser Permanente, Dept Pediat, San Francisco, CA USA