Pre-natal exposure to paracetamol and risk of wheezing and asthma in children: a birth cohort study.

BACKGROUND Paracetamol use has been associated with increased prevalence of asthma in children and adults, and one study reported an association between pre-natal exposure to paracetamol and asthma in early childhood. METHODS To examine if pre-natal exposure to paracetamol is associated with the risk of asthma or wheezing in early childhood, we selected 66 445 women from the Danish National Birth Cohort for whom we had information on paracetamol use during pregnancy and who participated in an interview when their children were 18-months-old and 12 733 women whose children had reached the age of 7 and estimated the prevalence of physician-diagnosed asthma and wheezing at the ages of 18 months and 7 years. We also linked our population to the Danish National Hospital Registry to record all hospitalizations due to asthma up to age of 18 months. RESULTS Paracetamol use during any time of pregnancy was associated with a small but statistically significant increased risk of physician-diagnosed asthma or bronchitis among children at 18 months [relative risk (RR) = 1.17, 1.13-1.23)], hospitalizations due to asthma up to 18 months (hazard ratio = 1.24, 1.11-1.38) and physician-diagnosed asthma at 7 years (RR = 1.15, 1.02-1.29). The highest risks were observed for paracetamol use during the first trimester of pregnancy and persistent wheezing (wheezing at both 18 months and 7 years) (RR = 1.45, 1.13-1.85). CONCLUSION Paracetamol use during pregnancy was associated with an increased risk of asthma and wheezing in childhood. If this association is causal, we may need to revisit the clinical practice on use of paracetamol during pregnancy.