1. Division of Maternal–Fetal Medicine, Department of Obstetrics and Gynecology Keck School of Medicine, University of Southern California Los Angeles CA USA
2. Fetal Diagnostic Centers Pasadena CA USA
3. Department of Obstetrics and Gynecology David Geffen School of Medicine, UCLA Los Angeles CA USA
4. Department of Obstetrics and Gynecology Wayne State University Detroit MI USA
5. Childbirth Research Associates North Hollywood CA USA