1. Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, San Francisco, CA 94143, USA
2. Fertility and Infertility Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
3. Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control, Atlanta, GA 30341, USA
4. Male Reproductive Medicine and Surgery, Department of Urology, Stanford University, School of Medicine, Stanford, CA 94305, USA