[1] University of California San Francisco School of Medicine,Department of Epidemiology and Biostatistics
[2] University of California San Francisco School of Medicine,Department of Obstetrics, Gynecology and Reproductive Sciences
[3] University of Iowa School of Medicine,Department of Pediatrics
[4] University of California San Diego,Department of Pediatrics
[5] Stanford University School of Medicine,Department of Pediatrics
[6] University of Iowa,Department of Epidemiology
[7] College of Public Health,California Preterm Birth Initiative
[8] University of California San Francisco School of Medicine,undefined