1. Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, California;
2. Departments of Epidemiology, and
3. Biostatistics, University of Medicine & Dentistry of New Jersey–School of Public Health, Piscataway, New Jersey;
4. Department of Maternal-Fetal Medicine, Kaiser Permanente West Los Angeles Medical Center, Los Angeles, California; and
5. Department of Obstetrics-Gynecology, University of California, Irvine, California