Premature birth, maternal smoking and other risk factors - A case-control study

Abstract

Objectives: To analyze possible risk factors for premature birth (PB). Study Design: Case-control study. Setting: Maternity Ward of Hospital Santo André, Leiria. Participants: Mothers and newborn children in 2010. Methods: We analyzed the clinical files of mothers giving birth in 2010. We defined the cases as births occurring before 37 weeks gestational age. The controls were births occurring at 37 or more weeks gestational age and were selected by systematic random sampling. Variables studied included maternal age, duration of pregnancy, gender of the child, birth weight, type of delivery, smoking habits, maternal hypertension, previous premature birth, time from last pregnancy, maternal body mass index, maternal infection, drug abuse, previous cervical intervention, diabetes, thyroid dysfunction, twin pregnancy, alterations of amniotic fluid, cervical incompetence, placental disorders, and uterine malformation. Multivariate logistic regression model was used to calculate odds ratios (OR) with significance set at α = 0.05. PASW v.18 software was used. Results: Among 2279 childbirths in 2010, the proportion of premature births was 6.32%. The final sample had 136 cases of PB and 316 controls. There was a higher percentage of smokers amongst the cases of PB (11.8% vs 7%), with an OR=2, but this was not statistically significant (p=0.069). In the selected logistic regression model, the determinants of PB with statistical significance were placental disorders (OR 33.7), previous PB (OR 5.8), arterial hypertension (OR 5.1), maternal infection (OR 4), and maternal age (OR 1.1). Conclusions: The risk factors for premature birth found were consistent with those described in the literature. The association with smoking was not statistically significant probably due to the small sample size.