P16.11: Risk factors for preterm delivery differ between smokers and non‐smokers

Abstract

To study differences in the risk factors for preterm delivery between smokers and non-smokers. An obstetric database of 13473 live singleton pregnancies delivered at Nepean Hospital between 1998 and 2003 was studied. Preterm delivery was defined as birth occurring before 37 weeks. Pregnancy characteristics included in the analysis were age, parity, maternal lean and adipose weight, height, BMI, cigarette smoking and birthweight. Maternal lean body weight (LBW) and adipose mass was calculated from the Deurenberg formula. Logistic regression analysis was performed for smokers and non-smokers, to identify the significant predictors and corresponding odds ratios. Overall 7.8% of infants were born preterm (<37 weeks), with 6.7% being between 32 and 37 weeks. Normal BMI was found for 44.3% of cases. About 38.3% were primiparae, 27% were smokers. In non-smokers, significantly increased risk was noted with maternal age (OR 1.02 per year, 95% CI 1.001-1.035), and nulliparity (OR 1.21, 95% CI 1.03-1.44) only. In smokers, significantly increased risk was noted with maternal fat mass only (OR 1.09 per Kg, 95% CI 1.005-1.19). No correlations were noted between number of cigarettes smoked and risk. Maternal cigarette smoking is associated with changes in the risk factors for preterm delivery. The degree of obesity increases the risk for preterm delivery in smokers only, whereas in non-smokers nulliparity and age are the only risk factors.