Risk factors for spontaneous preterm birth: a Northern Italian multicenter case-control study

Preterm birth remains one of the most serious problems facing obstetricians. The aim of this study was to investigate the risk factors for spontaneous preterm birth in northern Italy. Nine different collaborating institutions participated in this multicenter case-control study. Cases were defined as women who were spontaneously delivered of a live singleton newborn between 20 and 37 weeks of gestation. One control was matched to each case by delivery date, maternal age and parity. Seven hundred and fifty-four cases and 754 controls were available for data analysis. Demographic and clinical characteristics were obtained using a standardized questionnaire. At the time of hospital admission, urine and cervico-vaginal samples were collected and tested for bacterial infections and bacterial vaginosis, respectively. Variables found to be statistically significant in the univariate analysis were entered in a multivariate model to examine their independent effects. In order of decreasing odds ratios (ORs), the factors that showed a significant association with preterm delivery were: previous preterm birth (OR 5.7, confidence interval (CI) 2.5-12.9); second-trimester miscarriages (OR 4.4, CI 1.3-15.3); genital bleeding before 24 weeks of gestation (OR 2.5, CI 1.6-3.8); bacterial vaginosis (OR 2.0, CI 1.3-3.1), and previous genital infections (OR 1.6, CI 1.1-2.5). This study confirms that infections play a role in the etiology of preterm birth and that reproductive history is still the most important factor in identifying women at increased risk.