1. Department of Epidemiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, Pennsylvania, USA
2. Department of Obstetrics, Gynecology and Reproductive Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
3. Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, San Francisco, California, USA
4. Department of Clinical Chemistry, Biomedicum, Helsinki University and Helsinki University Central Hospital, Helsinki, Finland
5. Institute of Reproductive and Developmental Biology, Imperial College of London, London, United Kingdom