European Journal of Obstetrics & Gynecology and Reproductive Biology
Maternal risk factors for preterm birth: a country-based population analysis
Introduction
Pre-term birth (PTB) is defined as birth before 37 completed weeks of gestation. Its incidence can vary depending on the geographical and demographic features of the population studied, and in Italy PTB comprises 6–7% of all births [1]. The precise role of events linked to an increased risk of PTB is largely unknown, but decidual hemorrhage, mechanical factors, hormonal changes and cervicovaginal infections have been associated with the pathophysiology of PTB [2], [3]. The incidence of PTB is rapidly growing, partly because today it includes some cases that in the past resulted in second trimester “late” abortions. The increase in industrialized countries is strongly linked to the rise of maternal age [4] and of the number of pregnancies following assisted reproductive treatments [5] as well as to the introduction of new risk factors related to life style [6].
It is nowadays important to investigate epidemiological and environmental factors to identify high risk women. The risk of PTB first of all correlates to intrinsic characteristics of the mother; it is different between racial and ethnic groups [7], [8] and is related to advanced maternal age [4]. In order to identify women at risk it is also important to assess maternal life style, level of education [6] and adequacy of prenatal care [9], [10], as well as employment-related psychological and physical stress [11], [12], [13]. Furthermore maternal BMI [14], [15], nutritional status, chronic diseases (such as hypertension, diabetes mellitus) [16], intrauterine malformation or infections, and endocrinological diseases have been linked with an increased risk of PTB.There is consistent evidence that having a history of PTB is the strongest predicting factor [17]. Previous abortion, independent of the type (spontaneous or induced), increases the possibility of PTB [18], [19]; moreover there is an increasing risk of very preterm birth associated with increasing numbers of abortions [20]. Pregnancies resulting from assisted reproductive treatment (IVF, ICSI) can increase the risk of PTB [5]. Similarly even an invasive diagnostic tool, such as amniocentesis or villocentesis, is demonstrated to be a potential risk factor [21], [22].
On the basis of these data it is clear that etiology of PTB is multi-factorial, and numerous exposures including social, psychological, biological and genetic factors are known to be associated. Results of studies coming from the “western world” not always are applicable from one situation to another. Nowadays in these countries there is also a lack of studies analyzing specific risk factors, so it would be necessary to make a distinction based on maternal origin and on different lifestyles. The aim of this study was to identify maternal risk factors for spontaneous PTB compared to delivery at term, in order to recognize high risk women and to provide a global overview of the Italian situation. The study sample comes from 9 different University Maternity Hospitals distributed throughout the country.
Section snippets
Materials and methods
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 (4 in the North: Milano, Modena, Torino, Trieste; 3 in the Centre: Ancona, Perugia, Siena; and 2 in the South: Catania, Foggia). The records related to deliveries occurring between April and December 2008. The study was reviewed and approved by the ethical committee of all the universities involved in the
Results
A total sample of 7634 women was recruited; 338 cases resulted in spontaneous PTB while 7296 women delivered at term. Table 1 reports descriptive statistics of each studied covariate, crossed also for multivariate. Of the total sample of 7634 women, 75% were <35 years old and 61.4% had BMI ≤ 25. In the sample there is an equal distribution regarding the type of employment whereas it results a low percentage of women smoking (10%) and women affected by diabetes mellitus (4%), chronic arterial
Discussion
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 [23]. In particular, mother's life style and mother's reproductive history play a role in the incidence of this event. It also results an increased risk in women with BMI > 25, confirming what it is described in the literature concerning a significant increase of the risk of PTB linked to the nutritional and metabolic
Acknowledgements
The study was financed by an unrestricted educational grant from Ferring SpA, Milan, Italy.
We are indebted with Professor Erminio Bonizzoni (University of Milan) for his valuable help in the statistical analysis of data.
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See Appendix A for participating centres and coordinators.