Prenatal and infant paracetamol exposure and development of asthma

Background: Prenatal and infant paracetamol exposure is proposed to increase the risk of asthma. Few previous studies addressed confounding by indication. Objective: To examine the association of prenatal and infant paracetamol exposure with asthma. Methods: We evaluated prenatal and infant paracetamol exposure in relation to current asthma at 36 months (N=53,169), current asthma at 7 years (N=25,394) and dispensed asthma medications at 7 years in the prescription registry (N=45,607) within the Norwegian Mother and Child Cohort Study. Log-binomial regression was used to calculate adjusted relative risks (adj.RR) and 95% confidence intervals (CI). We evaluated maternal respiratory infections/influenza, fever and pain during pregnancy as indications. To obtain further insight, we considered maternal paracetamol use outside pregnancy, maternal use of ibuprofen during pregnancy and paternal paracetamol use. Results: Prenatal paracetamol exposure was associated with asthma at 36 months, adj.RR 1.18 (95% CI: 1.10, 1.27), asthma at 7 years, adj.RR 1.30 (95% CI: 1.16, 1.45), and dispensed asthma medications at 7 years, adj.RR 1.18 (95% CI: 1.09, 1.29). Prenatal and infant paracetamol exposure showed independent associations with asthma. Furthermore, prenatal paracetamol exposure for any of the three indications yielded similar associations. Pain was the only indication associated with asthma independent of paracetamol use. There was no strong evidence of an association with maternal paracetamol use outside the pregnancy, prenatal ibuprofen exposure or paternal paracetamol use. Conclusion: Prenatal and infant paracetamol exposure was positively associated with asthma development.