[Idiopathic preterm deliveries in Denmark].

The objective of the study was to characterize and quantify various demographic factors in idiopathic preterm delivery. All women with a permanent address in Denmark with singleton pregnancies who gave birth to an infant in 1982 (n = 51,851) are included. The material was obtained by a linkage of the Medical Birth Register and the National Register of Hospital Discharges, using the personal identification number. The incidence of singleton preterm delivery was 4.5% (n = 2330) of which 67% (n = 1557) were idiopathic. Neonatal mortality rates were significantly lower in idiopathic compared to indicated preterm birth. Following stepwise logistic regression analysis, maternal age below 20 (adjusted odds ratio 1.63, 95% confidence interval (CI) 1.07-2.47; p < 0.03), maternal age above 30 (adjusted odds ratio 0.74, 95% CI 0.60-0.90; p < 0.004) and being married (adjusted odds ratio 0.63, 95% CI 0.43-0.94; p < 0.03) correlated with idiopathic preterm birth. It is concluded that idiopathic preterm birth is more common in single, young women and associated with lower neonatal mortality rate than indicated preterm birth.