1. Department of Obstetrics & Gynecology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
2. Department of Obstetrics, Gynecology, & Reproductive Biology, Harvard Medical School, Boston, MA 02115, USA
3. Division of Neonatology, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
4. Department of Pediatrics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA
5. Biomedical Library, University of Pennsylvania, Philadelphia, PA 19104, USA
6. Loyola University Chicago Stritch School of Medicine, Maywood, IL 60153, USA
7. Colby College, Waterville, ME 04901, USA
8. Department of Epidemiology, Harvard TH Chan School of Public Health, Boston, MA 02115, USA