1 Obstetrics and Gynecology, Baylor College of Medicine, Houston, TX. Electronic address: slclark@bcm.edu.
2 Wayne State University, Detroit, MI; Epidemiology and Biostatistics, Michigan State University, East Lansing, MI; Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI.
3 Obstetrics and Gynecology, Baylor College of Medicine, Houston, TX.