1. Obstetrix Collaborative Research Network; the Center for Research, Education, and Quality; Mednax National Medical Group; Sunrise FL USA
2. Julius Centre for Health Sciences and Primary Care; University Medical Centre Utrecht; Utrecht the Netherlands
3. Stanford Prevention Research Center; Stanford University; Stanford CA USA
4. Department of Obstetrics and Gynecology; University of Pittsburgh; Pittsburgh PA USA
5. Department of Obstetrics and Gynaecology; Academic Medical Centre Amsterdam; Amsterdam the Netherlands
6. Department of Obstetrics and Gynecology; University of California Irvine; Irvine CA USA
7. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD); Maternal-Fetal Medicine Units Network (MFMU); Bethesda MD USA
8. Department of Obstetrics and Gynecology; Alpert Medical School; Women & Infants Hospital; Brown University; Providence RI USA
9. Department of Epidemiology; School of Public Health; Brown University; Providence RI USA
10. The Biostatistics Center; George Washington University; Washington DC USA
11. Department of Obstetrics and Gynecology and Center for Women's Reproductive Health; University of Alabama at Birmingham; Birmingham AL USA
12. The Robinson Research Institute; School of Paediatrics and Reproductive Health; University of Adelaide, and The South Australian Health and Medical Research Institute; Adelaide SA Australia