1. Department of Gynecology and Obstetrics Johns Hopkins University School of Medicine Baltimore Maryland USA
2. Northwestern University Feinberg School of Medicine Chicago Illinois USA
3. Department of Medicine Columbia University Irving Medical Center New York New York USA
4. Department of Pediatrics Columbia University Irving Medical Center New York New York USA
5. Department of Obstetrics and Gynecology University of North Carolina at Chapel Hill School of Medicine Chapel Hill North Carolina USA
6. Department of Obstetrics and Gynecology Columbia University Irving Medical Center New York New York USA
7. Department of Mathematics and Statistics Middlebury College Middlebury Vermont USA