1. Department of Epidemiology & Biostatistics University of California San Francisco School of Medicine San Francisco California USA
2. UCSF California Preterm Birth Initiative University of California San Francisco School of Medicine San Francisco California USA
3. Department of Obstetrics, Gynecology and Reproductive Sciences University of California San Francisco School of Medicine San Francisco California USA
4. Department of Pediatrics University of California San Diego School of Medicine San Francisco California USA
5. School of Public Health Oregon Health & Science University and Portland State University Portland Oregon USA
6. Divisions of Biostatistics and Epidemiology, School of Public Health University of California Berkeley Berkeley California USA
7. Department of Obstetrics and Gynecology, Lundquist Institute for Biomedical Innovation at Harbor UCLA Medical Center University of California, Los Angeles Los Angeles California USA