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. Funding The Norwegian Mother and Child Cohort Study is supported by NIH (NIH/ NIEHS contract number N01-ES-75558, NIH/NINDS grant no. 1 UO1 NS 047537-01 and grant no. 2 UO1 NS 047537-06A1) and the Norwegian Research Council/FUGE (grant no. 151918/S10). Supported in part by the Intramural Research Program of the NIH, NIEHS (ZIA ES049019). Ms Magnus is also supported by the Norwegian Extra-Foundation for Health and Rehabilitation (grant no. 2011.2.0218).