Maternal risk factors for preterm birth: a country-based population analysis

Objective The aim of this study was to identify maternal risk factors for spontaneous preterm birth (PTB) compared to delivery at term, in order to recognize high risk women and to provide a global overview of the Italian situation. Study design A multicenter, observational and retrospective, cross-sectional study was designed. The study population comprised 7634 women recruited in 9 different University Maternity Hospitals in Italy. The main criteria for inclusion were: women having had vaginal preterm or term spontaneous delivery in each participating centre during the study period. The records related to deliveries occurring between April and December 2008. A multivariable logistic regression was employed to identify independent predictors of spontaneous preterm birth. Odds ratios (ORs) and 95% confidence intervals (95% CI) were reported with two-tailed probability ( p ) values. Statistical calculations were carried out using SAS version 9.1. A two-tailed p -value of 0.05 was used to define statistical significant results. Results A significant increased risk of PTB was found in women with BMI>25 (OR=1.662; 95% CI=1.033–2.676; p -value=0.0365) and in women employed in heavy work (OR=1.947; 95% CI=1.182–3.207; p -value=0.0089). Moreover there was a significant association between PTB and previous reproductive history. In fact a history of previous abortion (OR=1.954; 95% CI=1.162–3.285; p -value=0.0116) or previous cesarean section (OR=2.904; 95% CI=1.066–7.910; p -value=0.0371) was positively correlated to the increased risk of PTB and an important statistically significant association was calculated between PTB and previous pre-term delivery (OR=3.412; 95% CI=1.342–8.676; p -value=0.0099). All the other covariates examined as potential risk factors for PTB were not found to be statistically significantly related ( p -value>0.05). Conclusions The present study, applied to a substantial sample of Italian population, demonstrates that there are peculiar risk factors for spontaneous PTB in the Italian population examined. It shows an association between preterm delivery and certain maternal factors as: BMI, employment, previous abortions, previous PTBs and previous cesarean section.