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 interview3; this information should also have been taken into account.
With regard to the widespread use of NSAIDs4 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, 90% other anti-inflammatory agents) whereas 1276 used other drugs (11% psychotropic drugs, 10% systemic anti-infective agents), with an average of 2.2 drugs per woman (range 1-14).
In addition to a significant association between miscarriage and exposure to NSAIDs (table), a significant trend became apparent (χ2t = 10.54, P = 0.0011) for the number of drugs taken since the last menstruation. A logistic regression analysis using a backward stepwise selection then showed a significant association between number of drugs taken and miscarriage (odds ratio 1.15, 1.06 to 1.25), but not for use of NSAIDs.
Table 1.
Univariate analysis of spontaneous abortion risk in percentages (absolute numbers) related to characteristics of 1557 women studied
| Characteristic | Miscarriage | Relative risk (95% CI) | |
|---|---|---|---|
| (n=180) | (n=1377) | ||
| Use of NSAIDs | Yes | No | |
| Yes (n=281) | 16 (45) | 84 (236) | 1.51* (1.11 to 2.07) |
| No (n=1276) | 11 (135) | 89 (1141) | |
| Age (years) | |||
| ≤24 (n=105) | 10 (11) | 90 (94) | 1 |
| 25-9 (n=363) | 10 (35) | 90 (328) | 0.92 (0.48 to 1.75) |
| 30-4 (n=610) | 11 (66) | 89 (544) | 0.97 (0.53 to 1.77) |
| ≥35 (n=470) | 14 (65) | 86 (405) | 1.03 (0.56 to 1.89) |
| χ2t=3.1 | |||
| Smoked since last menstruation | |||
| Yes (n=238) | 10 (24) | 90 (214) | 0.85 (0.57-1.28) |
| No (n=1319) | 12 (156) | 88 (1163) | |
| Previous pregnancy | |||
| No (n=706) | 10 (71) | 90 (635) | 0.79 (0.59-1.04) |
| Yes (n=851) | 13 (109) | 87 (742) | |
| Previous miscarriage | |||
| Yes (n=205) | 11 (22) | 89 (183) | 0.92 (0.60-1.40) |
| No (n=1352) | 12 (158) | 88 (1194) | |
| No of drugs taken | |||
| 1 (n=713) | 9 (67) | 91 (646) | 1 |
| 2 (n=367) | 11 (39) | 89 (328) | 0.88 (0.61-1.29) |
| 3 (n=210) | 16 (34) | 84 (176) | 1.72 (1.17-2.53) |
| 4 (n=112) | 12 (13) | 88 (99) | 1.24 (0.71-2.16) |
| 5 (n=68) | 15 (10) | 85 (58) | 1.57 (0.85-2.90) |
| 6 (n=37) | 22 (7) | 78 (30) | 2.01 (0.99-4.07) |
| ≥ 7 (n=50) | 20 (10) | 80 (40) | 2.13 (1.17-3.88) |
| χ2t= 10.54* | |||
NSAIDs=non-steroidal anti-inflammatory drugs.
P<0.05.
Interpretation of data should include all possible confounding factors. In this case scant methodological approaches indicated exposure to NSAIDs early in pregnancy as a substantial risk factor for miscarriage, but only well designed studies and complete analysis can produce more concrete evidence.
Competing interests: None declared.
References
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