1. Department of Obstetrics, Gynecology and Reproductive Sciences, University of California San Diego, San Diego, CA, USA
2. Department of Obstetrics and Gynecology, Duke University, Durham, NC, USA
3. Department of Obstetrics and Gynecology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
4. Department of Obstetrics and Gynecology, The University of Alabama at Birmingham, Birmingham, AL, USA
5. RTI International, Raleigh, NC, USA
6. Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD, USA