1 Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, 4012 Old Clinic Building, Campus Box 7570, Chapel Hill, NC 27599-7570. Electronic address: antoinette_nguyen@med.unc.edu.
2 Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, 4012 Old Clinic Building, Campus Box 7570, Chapel Hill, NC 27599-7570.