Researchers in California interviewed 1,055 pregnant women immediately after their pregnancy was confirmed. They asked the women about their drug use since they became pregnant, their reproductive history, known or potential risk factors for miscarriage, and sociodemographic characteristics.
They found that use of NSAIDs during pregnancy increased the risk of miscarriage by 80%. The risk was much higher when NSAIDs were taken around conception or were used for longer than a week. Taking account of other factors, including drinking alcohol or coffee, did not change the results.
Aspirin was similarly associated with an increased risk of miscarriage but paracetamol was not, regardless of timing and duration of use.
All three drugs work by suppressing the production of prostaglandins (fatty acids needed for successful implantation of an embryo in the womb). Because NSAIDs and aspirin act on the whole body, they could lead to abnormal implantation that predisposes an embryo to miscarriage. In contrast, paracetamol acts only in the central nervous system, which may explain why it has no effect on risk of miscarriage, explain the authors.
These findings will need confirmation, say the authors. Meanwhile, it may be prudent for physicians and women who are planning to be pregnant to be aware of this potential risk and avoid using NSAIDs around conception.