title: Grandmother's smoking when pregnant with the mother and asthma in the grandchild: the Norwegian Mother and Child Cohort Study.
abstract: BACKGROUND
  A trans-generational influence of prenatal tobacco smoke exposure on asthma development has been proposed but the evidence remains sparse.
  
  
  METHODS
  We examined the grandmother's smoking when pregnant with the mother in relation to asthma outcomes in the grandchild (current asthma at 36 months (N=53 169, cases=3013), current asthma at 7 years (N=25 394, cases=1265) and dispensed asthma medications at 7 years in the Norwegian Prescription Database (N=45 607, cases=1787)) within the Norwegian Mother and Child Cohort Study (MoBa). We calculated adjusted RR (adj. RR) and 95% CIs using log binomial regression.
  
  
  RESULTS
  A total of 23.5% of mothers reported that their mother smoked when pregnant with them. The grandmother's smoking when pregnant with the mother was positively associated with asthma at 36 months (adj. RR 1.15 (95% CI 1.06 to 1.24)), asthma at 7 years (adj. RR 1.21 (95% CI 1.07 to 1.37)) and dispensed asthma medications at 7 years (adj. RR 1.15 (95% CI 1.04 to 1.26)). This positive association did not differ significantly by the mother's smoking status when pregnant with the child (p values for multiplicative interaction >0.1).
  
  
  CONCLUSIONS
  The grandmother's smoking when pregnant with the mother increased the risk of asthma in the grandchild independent of the mother's smoking status. However, given limited information on the grandmother's socioeconomic status, asthma status and other factors, unmeasured confounding may be present.
authors.affiliation: Division of Epidemiology, Department of Chronic Diseases, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Magnus
authors.affiliation: Norwegian Institute of Public Health, Institute Management and Staff, Oslo, Norway.
authors.forename: Siri E
authors.initials: SE
authors.lastname: Håberg
authors.affiliation: Division of Epidemiology, Department of Pharmacoepidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Karlstad
authors.affiliation: Division of Epidemiology, Department of Chronic Diseases, Norwegian Institute of Public Health, Oslo, Norway Medical Faculty, Department of Community Medicine, University of Oslo, Oslo, Norway.
authors.forename: Per
authors.initials: P
authors.lastname: Nafstad
authors.affiliation: Epidemiology Branch, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: London
authors.affiliation: Division of Epidemiology, Department of Chronic Diseases, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Wenche
authors.initials: W
authors.lastname: Nystad
mesh_terms: D000328:Adult; D001249:Asthma / Q000188:drug therapy / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D015988:Cohort Effect; D015986:Confounding Factors, Epidemiologic; D016208:Databases, Factual; D011307:Drug Prescriptions / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D009035:Mothers / Q000706:statistics & numerical data*; D009664:Norway / Q000453:epidemiology; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000453:epidemiology*; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*
keywords: Asthma; Tobacco and the lung