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EDITOR-The finding of Li et al of an association between an increased risk of miscarriage and use of non-steroidal anti-inflammatory drugs (NSAIDs) relies on biased data. 1 For the same cohort of women, previous analysis showed that exposure to magnetic fields was a risk factor for miscarriage, 2 and this variable should have been included. Moreover, 103/170 women had already had a miscarriage at the time of the interview 3 ; this information should also have been taken into account.
With regard to the widespread use of NSAIDs 4 a cohort study was performed on 1557 pregnant women (gestational age < 20 weeks) who contacted a drug information centre was performed, collecting follow up data on pregnancy outcome after delivery. 5 The NSAID users were 281 (10% aspirin,...