1. Department of Epidemiology and Biostatistics; Global Health Sciences and the Preterm Birth Initiative; University of California San Francisco; San Francisco California USA
2. Department of Public Health; Brown University; Providence Rhode Island USA
3. Department of Epidemiology and Biostatistics and the California Preterm Birth Initiative; University of California San Francisco; San Francisco California USA
4. California Preterm Birth Initiative; University of California San Francisco; San Francisco California USA
5. Department of Pediatrics; University of California San Diego; La Jolla California USA
6. Departments of Epidemiology and Pediatrics; University of Iowa; Iowa City Iowa USA
7. Department of Pediatrics and the California Preterm Birth Initiative; University of California San Francisco; San Francisco California USA
8. Department of Epidemiology and Biostatistics, Pediatrics and the California Preterm Birth Initiative; University of California San Francisco; San Francisco California USA
9. Institute for Human Genetics; University of California San Francisco; San Francisco California USA