1National Institutes of Health, National Institute of Child Health and Human Development/Division of Epidemiology, Statistics and Prevention Research, Department of Health and Human Services, Bethesda, Maryland
2Department of Obstetrics and Gynecology, Oregon Health and Sciences University, Portland, Oregon
3Department of Obstetrics and Gynecology, Maricopa Integrated Health System and Medical Professionals of Arizona, Phoenix
Reprints or correspondence: Dr. Mark A. Klebanoff, National Institutes of Health, NICHD/DESPR, 6100 Executive Blvd., Rm. 7B05, MSC 7510, Bethesda, MD 20892 ([email protected]).