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Effects of smoking in pregnancy on neonatal lung function

AIMS To assess the effects of smoking during pregnancy on lung mechanics and lung volumes in the immediate neonatal period, before infants are exposed to passive smoking. METHODS Lung function tests were carried out within 72 hours of delivery in infants born to 100 non-smoking and 189 smoking mothers. Lung growth was assessed by plethysmography and lung mechanics using the single breath occlusion technique and oesophageal balloon/ pneumotachography. Antenatal maternal serum cotinine values were obtained from 133 mothers. RESULTS Smoking was associated with a significant reduction in birthweight (mean 256 g, 95% CI 0.164 to 0.392), and length (mean 1.26 cm, 95% CI 0.48 to 2.00). Lung volume was not reduced when related to weight. Smoking was associated with a highly significant reduction in static compliance (Crs). This effect remained significant after relating Crs to weight and lung volume. Regression analyses showed that the Crs association was limited to the boys. Smoking was associated with a small but significant reduction in respiratory system conductance (Grs) (single breath occlusion technique) and total pulmonary conductance (Gp). These associations were limited to girls. CONCLUSIONS Smoking in pregnancy reduces static compliance in boys and conductance in girls. There was no evidence that maternal smoking adversely affected fetal lung growth. Key messages • Smoking during pregnancy has an adverse effect on birthweight, length, head and chest circumference • The lungs of boys but not girls infants born to smoking mothers have reduced compliance • The lungs of girls but not boys born to smoking mothers have increased airways resistance, possibly due to the growth suppression effect • Pulmonary hypoplasia is not responsible for the increase in respiratory symptoms associated with antenatal smoking