1. Department of Epidemiology; Graduate School of Public Health, University of Pittsburgh; Pennsylvania USA
2. Department of Obstetrics, Gynecology, and Reproductive Sciences, School of Medicine; University of Pittsburgh; Pennsylvania USA
3. Magee-Womens Research Institute; Pittsburgh Pennsylvania USA
4. Division of Epidemiology, School of Public Health; University of California; Berkeley California USA
5. Department of Epidemiology, Biostatistics and Occupational Health; McGill University; Montréal Quebec Canada