1. Division of Reproductive Endocrinology and Infertility (D.K.S.), Department of Obstetrics and Gynecology, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242;
2. Division of Reproductive Endocrinology and Infertility (S.A.M., K.F.B.C., E.S.G.), Department of Obstetrics, Gynecology, Boston, Massachusetts 02115
3. Reproductive Biology, Brigham and Women's Hospital and Harvard Medical School, Channing Laboratory (S.A.M.), Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115
4. Harvard Medical School, and Department of Epidemiology (S.A.M.), Harvard School of Public Health, Boston, Massachusetts 02115