1. Department of Obstetrics and Gynecology , Seoul National University College of Medicine , Seoul , Korea
2. Department of Obstetrics and Gynecology , Seoul National University Bundang Hospital , Seongnam-si , Korea
3. Department of Obstetrics and Gynecology , Yonsei University College of Medicine , Seoul , Korea
4. Perinatology Research Branch, NICHD/NIH/DHHS , Bethesda, MD, USA , and Detroit, MI , USA
5. Department of Obstetrics and Gynecology , University of Michigan , Ann Arbor, MI , USA
6. Department of Epidemiology and Biostatistics , Michigan State University , East Lansing, MI , USA
7. Center for Molecular Medicine and Genetics , Wayne State University , Detroit, MI , USA