title: Maternal smoking and birthweight: effect modification of period, maternal age and paternal smoking.
abstract: OBJECTIVE
  To study the effect on birthweight of maternal smoking, and its modification by study period, maternal age and paternal smoking.
  
  
  METHODS
  A retrospective questionnaire based national survey comprising a random sample (n=34,799) of all mothers giving birth in Norway 1970-91. Variables studied were parental smoking during pregnancy, birthweight, maternal age and infant's year of birth.
  
  
  RESULTS
  The overall difference in mean birthweight between non-smoking and smoking mothers was 197 g. The difference in birthweight between non-smoking and smoking mothers increased with maternal age from 182 g (<20 years of age) to 232 g (35+ years of age). There was no significant effect of paternal smoking on birthweight when the mother was a non-smoker. When the mother was a smoker and the father was a non-smoker, the birthweight, adjusted for maternal age, was reduced by 153 g (p<0.005). However, when both parents smoked, the birthweight, adjusted for maternal age, was reduced by 201 g (p<0.0005). Even though the prevalence of paternal smoking decreased by 38% during the study period, there was no significant increase in overall mean birthweight. IMPLICATION AND RELEVANCE OF RESULTS: The negative effect of maternal smoking on birthweight appears to increase with maternal age. For a non-smoking pregnant woman to live with a smoking partner has little, if any, effect on birthweight. The negative effect of paternal smoking was only observed when the mother was smoking and might reflect two possible mechanisms: (1) that a smoking mother has a greater cigarette consumption when the partner also smokes, and (2) that a smoking mother is less concerned about passive smoking than a non-smoking mother.
authors.affiliation: Department of Public Health and Primary Health Care, University of Bergen, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Haug
authors.forename: L M
authors.initials: LM
authors.lastname: Irgens
authors.forename: R
authors.initials: R
authors.lastname: Skjaerven
authors.forename: T
authors.initials: T
authors.lastname: Markestad
authors.forename: V
authors.initials: V
authors.lastname: Baste
authors.forename: P
authors.initials: P
authors.lastname: Schreuder
mesh_terms: D000328:Adult; D001724:Birth Weight; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D018811:Maternal Exposure; D009664:Norway / Q000453:epidemiology; D018812:Paternal Exposure; D011247:Pregnancy; D012189:Retrospective Studies; D012907:Smoking / Q000009:adverse effects*; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
chemical_list: D014028:Tobacco Smoke Pollution