Longitudinal study of childhood wheezy bronchitis and asthma: outcome at age 42

the timing of the data collection, our information could not be biased by the women's knowledge about the outcome of pregnancy.Potential misclassification is likely to be non-differential, and our results may thus underestimate the true association between coffee drinking and stillbirth.Due to a higher intake of coffee and a faster metabolism among smokers 15 16 we hypothesised that the fetotoxic effect of caffeine could depend on smoking habits during pregnancy.However, the risk of stillbirth associated with coffee was similar in smokers and non-smokers.There did not seem to be one single cause that could explain the increased risk of stillbirth among women with a high intake of coffee (see bmj.com).Information on coffee intake during pregnancy was missing in a quarter of the population.Women with missing information had a different risk profile than women with valid information.However, we have no reason to believe that the association between coffee and stillbirth among women with non-valid information would be different from the one we found.We thank Morten