[1] Univ Washington, Sch Med, Dept Obstet & Gynecol, Seattle, WA 98195 USA
[2] Univ Washington, Surg Outcomes Res Ctr, Sch Med, Seattle, WA 98195 USA
[3] Univ Washington, Sch Publ Hlth & Community Med, Dept Epidemiol, Seattle, WA 98195 USA
[4] Univ Washington, Dept Surg, Sch Med, Seattle, WA 98195 USA