[1] Univ Michigan, Sch Publ Hlth, Dept Hlth Policy & Management, Ann Arbor, MI 48109 USA
[2] Columbia Univ, Mailman Sch Publ Hlth, Averting Maternal Death & Disabil Program, New York, NY USA
[3] Univ Michigan, Sch Publ Hlth, Dept Epidemiol, Ann Arbor, MI 48109 USA
[4] Columbia Univ, Dept Epidemiol, Mailman Sch Publ Hlth, New York, NY USA