Prenatal paracetamol exposure and asthma: further evidence against confounding

Observational studies have reported an association between maternal use of paracetamol in pregnancy and childhood asthma, which was not explained by measured confounding factors. However, it is possible that this relation might be confounded by unmeasured behavioural factors linked to paracetamol usage; if that were the case, effects of similar magnitude of partner's paracetamol use and/or postnatal maternal use would be expected.

In the Avon Longitudinal Study of Parents and Children (ALSPAC), a population-based birth cohort, we compared the univariate effects of maternal use of paracetamol in pregnancy on risk of doctor-diagnosed asthma, wheeze and elevated immunoglobulin E (IgE) in the offspring at 7 years of age, with the univariate effects of partner's use and postnatal maternal use on these phenotypes.

Maternal use of paracetamol in pregnancy was strongly associated with all outcomes. Partner's use was very weakly associated with asthma but not associated with wheezing or IgE. Postnatal maternal use was associated with asthma and wheezing, though less strongly than was prenatal use, and was not associated with IgE. On mutual adjustment, the effects of maternal use in pregnancy on all outcomes were not substantially attenuated, whereas the effects of partner's use on asthma, and of postnatal maternal use on asthma and wheezing, were reduced.

These findings suggest that the relation between maternal use of paracetamol in pregnancy and childhood asthma is unlikely to be confounded by unmeasured behavioural factors linked to paracetamol use.