1. Division of Maternal-Fetal Medicine, Obstetrix Medical Group of Washington, Seattle, WA, USA
2. Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Diego, San Diego, CA, USA
3. Department of Obstetrics and Gynecology, Duke University Medical Center, Durham, NC, USA
4. Department of Biostatistics and Bioinformatics, Duke University School of Medicine, Durham, NC, USA
5. Department of Obstetrics, Gynecology, and Reproductive Sciences, Division of Maternal-Fetal Medicine, University of California, San Francisco, San Francisco, CA, USA