EFFECTS OF MATERNAL SMOKING DURING PREGNANCY AND A FAMILY HISTORY OF ASTHMA ON RESPIRATORY-FUNCTION IN NEWBORN-INFANTS

Introduction Infants of mothers who smoke have reduced respiratory fun ction and are more likely to develop wheezing, Little evidence is avai lable on the effect of inutero cigarette-smoke exposure as opposed to postnatal exposure to environmental tobacco smoke, We used a previousl y validated non-invasive method to measure the time to peak tidal expi ratory flow (tPTEF) as a proportion of expiratory time (tE) in newborn infants soon after birth to examine the effects of a family history o f asthma and in-utero cigarette-smoke exposure on the infants' respira tory function. Methods We collected respiratory-function data from 500 healthy infants of mothers taking part in the Western Australia Pregn ancy Cohort Study, During behaviourally defined quiet sleep, measureme nts were obtained a median of 58 h (range 26-159) after the infants we re born, We used uncalibrated inductance plethysmography. The uncalibr ated volume signal was differentiated to flow and used to calculate re spiratory rate, total inspiratory time, tE, and tPTEF, Mothers answere d questionnaires on demographic, medical, and pregnancy characteristic s, including smoking history. Serum cotinine measurements were availab le to validate self-reported smoking history in a subset of mothers (2 38). Results Data suitable for analysis were obtained from 461 infants . In multivariate regression analysis, lower values of tPTEF/tE were i ndependently associated with respiratory rate (beta coefficient per 10 breaths/min 0.018 [SE 0.005], p<0.01), age (beta coefficient per 10 h -0.008 [0.003], p<0.01), maternal smoking during pregnancy (>10 cigar ettes daily; beta coefficient -0.049 [0.022], p<0.05), maternal hypert ension during pregnancy (-0.037 [0.015], p<0.02), and a family history of asthma (-0.028 [0.014], p<0.05). Conclusions In-utero smoke exposu re, a family history of asthma, and maternal hypertension during pregn ancy are associated with reduced respiratory function after birth. We speculate that these factors adversely affect lung development in uter o.