Immigrants and preterm births: a nationwide epidemiological study in Sweden.

To examine, nationwide, if there is an association between country of birth in mothers and preterm birth and to study whether any such association remains in second-generation immigrant women. In this follow-up study, a nationwide research database located at Lund University, Sweden, was used to identify all preterm born singletons in Sweden between January 1, 1982, and December 31, 2006. Incidence ratios were standardized with regard to maternal age at birth, marital status, geographical region, body height, and smoking history as well as period of birth, family income, and gender of the infant. Singletons of mothers born in Sweden were used as the reference group. There were 2,192,843 records for singletons over the study period, of whom 4.9 % were preterm births and 0.8 % were very preterm births. Increased risk of preterm birth was observed for mothers from Austria, Yugoslavia, Romania, Central Europe, and Asia. Increased risk of very preterm birth was observed for mothers from Eastern Europe, Central Europe, Africa, and Asia; these increased risk disappeared, however, in the second-generation female immigrants. Country of birth in mothers affected the risk of preterm birth; maternity care should pay special attention to women from certain population groups.