Fertility Blog

Don't Panic Over Aspirin

A new study, just published in the British Medical Journal has received quite a bit of press attention. This study, conducted at Kaiser Permanente in Northern California, suggests there may be a relationship between the use of aspirin and aspirin- like medications (called non-steroidal anti-inflammatory drugs, or NSAIDs) and first trimester miscarriage. We at PFC took a closer look at the study and determined that it has severe shortcomings.

NSAIDs, including aspirin, ibuprofen, naproxen and others, have not as yet been strictly forbidden during pregnancy, although most doctors, PFC physicians included, recommend acetaminophen (Tylenol) if needed for headaches and other minor ailments during pregnancy.

Research has long established the impact of aspirin on women trying to get pregnant. At low doses (e.g. 81 mg), aspirin has markedly different effects on such things as platelet function as compared to higher doses (325-1000 mg). At low doses, some studies have suggested that aspirin may improve uterine blood flow and enhance embryo implantation. At higher doses, NSAIDs may inhibit prostaglandins, substances important for ovulation and implantation. This is the basis upon which we, at PFC, have designed our medication treatment protocol. We suggest patients not take drugs such as ibuprofen and naproxen during treatment, yet we do recommend patients undergoing infertility treatment take a daily baby aspirin.

This recent study surveyed 1055 women immediately after their pregnancy was diagnosed, and the women were followed up to 20 weeks of pregnancy. Only 53 women reported using NSAIDs around the time of conception or during pregnancy (5% of those surveyed). Of these, 15 (25%) miscarried. Of the 980 women who reportedly did not use NSAIDs, 149 (15%) miscarried. The 95% confidence interval was 1.0-3.2. When the 95% confidence interval is less than 1.0, the results are not considered statistically significant. Therefore, these results just barely achieved statistical significance. If the study had been able to find more women who had used NSAIDs, it might be more conclusive.

With so few women reporting NSAID use, and with results barely in the statistically significant range, more questions than answers are raised. It is disappointing that the authors did not include the average age of the mothers in their data presentation. Miscarriage is strongly associated with maternal age, as more embryos are genetically abnormal and will likely miscarry, as the mother is older at conception. Is there a possibility that the average age of the women using NSAIDs was greater, by chance or not? The study did not specify the maternal ages or how the data was adjusted to eliminate this potential important bias.

However cautiously we must review these results, PFC will continue to recommend a daily dose of baby aspirin to our patients undergoing infertility treatment. At such a low dose, baby aspirin improves uterine blood flow and this study does not warrant alarm. The primary conclusion from this Kaiser study strongly suggests that further research is needed.

Posted on September 14th, 2003

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