1. Section of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
2. Convergent Engineering, Newberry, Florida
3. Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama
4. Departments of Biostatistics and Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama