[1] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Epidemiol, Pittsburgh, PA 15261 USA
[2] Univ Pittsburgh, Magee Womens Res Inst, Pittsburgh, PA 15260 USA
[3] Univ Pittsburgh, Dept OB GYN & Reprod Sci, Pittsburgh, PA 15260 USA
[4] NIA, Lab Epidemiol Demog & Biometry, Bethesda, MD 20892 USA
[5] Univ Calif San Francisco, Dept Obstet & Gynecol, San Francisco, CA 94143 USA
[6] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[7] Univ Wisconsin, Dept Kinesiol, Madison, WI USA
[8] Univ Tennessee, Memphis, TN USA