The aim of this study was to assess the frequency and risk factors of Preterm birth (PB), depending on the mechanism of their occurrence in nulliparous women with singleton pregnancies. Methods and Results: This retrospective, population-based cohort study included 327 nulliparous women who gave birth at 22-37 weeks gestation. Three groups of women were formed: Group 1 included 32 women with spontaneous PB, Group 2 included 115 women with preterm premature rupture of membranes (PROM), and Group

more »

... 3 included 180 women with medical indication for PB. The average age of the mothers for the whole group was 29.3±6.0 years. Depending on the gestational age, PB in 22-27 weeks occurred in 23(7.4%) cases, 28-33 weeks in 110(33.6%) cases, and 34-37 weeks in 194(59%) cases. In our cohort, the frequency of PB resulting from spontaneous PB, PROM or medical indication for PB was 9.8%, 35.2%, and 55%, respectively. The main risk factors for PB were preeclampsia of varying severity, placental abruption, placental insufficiency, and fetal growth retardation. The highest number of pregnancy complications was found in Group 3. Conclusion: PB in nulliparous women occurs more often in the period of 34-37 weeks, the main reason being medical indications (maternal or fetal). Attempts to analyze, interpret, and reduce the level of PB should be considered separately, depending on the mechanism of their occurrence.