1. School of Medicine, Vanderbilt University, Nashville, Tennessee.
2. Department of Obstetrics, Gynecology, and Reproductive Sciences, Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, Pennsylvania.
3. Department of Obstetrics and Gynecology, The Ohio State University Medical College, Columbus, Ohio.
4. Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania.
5. Clinical and Translational Research Institute, University of Pittsburgh, Pittsburgh, Pennsylvania.