Active smoking and environmental tabacco smoke (ETS) exposure in pregnancy and preterm/very preterm delivery: a multicentric italian study

Introduction: Smoking during pregnancy is a well recognized risk of preterm delivery while ETS exposure is still questionable. The aim of this study is to assess the relationship between active smoking and ETS exposure with preterm/very preterm delivery.Methods: A case control study was carried out in Italy during October 1999 and September 2000 in nine cities. Singleton babies born between 26th and 37th week were considered as cases (among them, babies born between 26th and 35th week were considered very preterm cases). Controls (babies of gestational age >37th week) were enrolled among singleton births occurred in the same hospitals within a few days after the case delivery. A total of 299 preterm cases (including 105 very preterm) and 855 controls were considered. A self-administrated questionnaire was used to assess exposure.Results: The prevalence of active smoking during pregnancy was 14.8% among controls and 20.2% among cases. ETS exposure (yes/no) during pregnancy was reported in 34.7% of controls and 37.4% of cases. Multivariate logistic regression analysis was carried out adjusting for maternal age, previous preterm deliveries, miscarriages, and hypertension. A relationship was observed between active smoking during pregnancy and preterm/very preterm delivery (adjusted ORs: 1.58; 95%CI 1.10-2.28 and 2.06; 1.21-3.51, respectively). A dose-response relationship according to the number of cigarettes/day (none, < 10 and > 10) was observed (adjusted ORs: 1. 54 and 1.69 for preterm babies and 1.90 and 2.46 for very preterm babies). No association was observed between ETS exposure and preterm delivery on the whole, while when taking into account the subset of very preterm cases, the adjusted OR is 1.66 (95% CI 1.06-2.59) with a dose response according to the number of cohabitant smokers (none, 1, 2 or more subjects) (Adjusted ORs 1.47 and 3.57 respectively). When classifying, considering both active smoking and ETS exposure (no active smoking/no ETS exposure as referent) ETS exposure in non-smokers is associated with very preterm delivery (Adjusted OR 1.70; 95% CI: 1.01-2.86).Discussion: Smoking during pregnancy is strongly associated with preterm delivery, with a dose-response. ETS exposure in non-smoker women is associated with very preterm delivery only.