1. Reproductive Endocrinology and Infertility, University of North Carolina Chapel Hill , NC, USA
2. Reproductive Partners—San Diego , La Jolla, CA, USA
3. Department of Obstetrics and Gynecology, University of California San Diego , La Jolla, CA, USA
4. Epidemiology Branch, National Institute of Environmental Health Sciences , Durham, NC, USA
5. Westat , Durham, NC, USA
6. Department of Obstetrics and Gynecology, Duke University , Durham, NC, USA