1. Department of Pediatrics University of California San Diego La Jolla California USA
2. The California Preterm Birth Initiative University of California San Francisco San Francisco California USA
3. Department of Epidemiology and Biostatistics University of California San Francisco San Francisco California USA
4. Department of Obstetrics, Gynecology and Reproductive Sciences University of California San Francisco California USA
5. Departments of Nursing and Institute for Human Genomics University of California San Francisco California USA
6. San Francisco Department of Public Health San Francisco California USA
7. Departments of Epidemiology and Pediatrics University of Iowa Iowa City Iowa USA