To Örebro University

Background: Previous studies have found associations between smoking during pregnancy (SDP) and childhood asthma/wheeze. Although nicotine has been suggested as a causal agent, the mechanism is unclear. In Sweden, oral moist snuff (snus) is a common form of tobacco, with high nicotine levels, but no combustion.

Aim: To estimate the association between tobacco use in pregnancy, both smoking and snus, and asthma/wheeze in the child, to examine the role of nicotine.

Methods: Our cohort included 897 975 children, born in Sweden 2005-2012. Information on SDP and snus use came from the Medical Birth Registry. We based the asthma/wheeze outcome on diagnoses and drugs from national health registers, as incident asthma at age 0-7 yrs and prevalent asthma at ages 2-6 yrs.

Results: For the association of SDP and asthma/wheeze, we saw a pattern with higher hazard ratios around 5 and 18 months of age (Figure 1). Snus did not show the same pattern. Prevalent asthma, showed the strongest association with SDP at age 2 yrs (adjOR=1.22 95% CI: 1.17-1.28). The corresponding estimates for snus was adjOR=1.06 (95% CI: 0.96-1.18).

Conclusion: We saw an association between SDP and asthma at early age, but the association with snus was much weaker. The results suggest that nicotine is not a causal agent in the SDP – asthma association.