[1] Stanford Univ, Sch Med, Dept Urol, Stanford, CA 94305 USA
[2] Stanford Univ, Sch Med, Dept Obstet, Stanford, CA 94305 USA
[3] Stanford Univ, Sch Med, Dept Gynecol, Stanford, CA 94305 USA
[4] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Div Intramural Populat Hlth Res, Rockville, MD 20852 USA