Socio-economic risk factors for preterm birth in Norway 1999–2009

Aims: Preterm birth is a major cause of perinatal mortality and morbidity and is strongly associated with socio-economic factors. The objective of this study was to examine the associations of maternal education, marital status and ethnicity with preterm birth and to determine the extent to which such associations can be explained by the established risk factors of maternal age, parity and smoking. Methods: This was a register-based cohort study with data from the Medical Birth Registry of Norway 1999–2009 and Statistics Norway. The sample included all singleton spontaneous births in Norway from 1999 to 2009 (n=494,073). The main outcome measure was preterm birth (gestational age