1. Department of Pediatrics , Vagelos College of Physicians and Surgeons, Columbia University , New York, NY , USA
2. Department of Pediatrics and Microbiology , New York University School of Medicine, 317 East 34th St, Suite 902 , New York, NY 10016 , USA , Tel.: 646-754-1041
3. George Washington University Biostatistics Center , Washington, DC , USA
4. Department of Obstetrics and Gynecology , University of Cincinnati , Cincinnati, OH , USA
5. Department of Obstetrics and Gynecology , University of Alabama at Birmingham , Birmingham, AL , USA
6. Department of Obstetrics and Gynecology , University of Texas Southwestern Medical Center , Dallas, TX , USA
7. Pregnancy and Perinatology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development , Bethesda, MD , USA
8. Department of Obstetrics and Gynecology , University of Utah , Salt Lake City, UT , USA
9. Department of Obstetrics and Gynecology , University of North Carolina at Chapel Hill , Chapel Hill, NC , USA
10. Department of Obstetrics and Gynecology , Case Western Reserve University-MetroHealth Medical Center , Cleveland, OH , USA
11. Department of Obstetrics and Gynecology , Northwestern University , Chicago, IL , USA
12. Department of Obstetrics and Gynecology , University of Texas Health Science Center at Houston , Houston, TX , USA
13. Department of Obstetrics and Gynecology , Brown University , Providence, RI , USA
14. Department of Obstetrics and Gynecology , The Ohio State University , Columbus, OH , USA
15. Department of Obstetrics and Gynecology , Drexel University , Philadelphia, PA , USA
16. Department of Obstetrics and Gynecology , Oregon Health and Science University , Portland, OR , USA
17. Department of Obstetrics and Gynecology , University of Texas Medical Branch , Galveston, TX , USA
18. Department of Obstetrics and Gynecology , Wayne State University , Detroit, MI , USA