1. Department of Obstetrics/Gynecology, University of Pennsylvania, Philadelphia, Pennsylvania.
2. Department of Psychiatry, University of Pennsylvania, Philadelphia, Pennsylvania.
3. Center for Clinical Epidemiology and Statistics, University of Pennsylvania, Philadelphia, Pennsylvania.
4. Department of Mathematics, Statistics and Computer Science, St. Olaf College, Northfield, Minnesota.
5. Center for Research in Reproduction and Women's Health, University of Pennsylvania, Philadelphia, Pennsylvania.