The Effect of Aspirin on Miscarriage Risk

Smiling woman taking medication
BDLM/Getty Images

There's a lot of conflicting information about the safety of using aspirin during pregnancy. Some sources say it can increase your risk of miscarriage, whereas others say the opposite. Which is correct? Possibly both. There isn't much current research on aspirin and miscarriage risk. However, a review published in 2014 found previous studies to be of varying quality but concluded there's no benefit to taking aspirin, or other coagulants, anyway.

How Aspirin Could Increase Miscarriage Risk

A handful of studies have linked the class of painkillers known as non-steroidal anti-inflammatory drugs (NSAIDs), which includes aspirin as well as pretty much every over-the-counter painkiller except Tylenol, with miscarriage. A 2001 study came up with the particularly striking finding that NSAIDs during pregnancy increased the risk of miscarriage by as much as 80%.

A separate 2003 study replicated the findings, noting that NSAIDs were related to miscarriage whereas Tylenol was not, leading the authors to speculate that the NSAIDs themselves could potentially be causing the miscarriages.

But a 2006 study found no evidence of an association between aspirin during pregnancy and miscarriage -- so the truth isn't yet clear. It could be that some other factor is responsible for the association found in the first studies. (For example, it could be that whatever condition leads women to use NSAIDs would actually be the factor increasing risk of miscarriage.) Right now, however, doctors tend to lean toward Tylenol as the safest painkiller choice for pregnancy.

How Aspirin Could Reduce Miscarriage Risk

It sounds like a contradiction to say that aspirin can reduce the risk of miscarriage right after saying it's best to avoid using it during pregnancy. The answer is the dosage and reason for usage.

There's no evidence that aspirin has any benefit for the average pregnant woman, but one study published in 2008 suggested low-dose aspirin can be useful for women who have had recurrent miscarriages associated with antiphospholipid syndrome or other blood clotting disorders.

Doctors often prescribe "baby" aspirin in combination with heparin to prevent miscarriage in women with these conditions, and some doctors recommend aspirin to some women who have had unexplained recurrent miscarriages.

But in this kind of a protocol, the dose of aspirin is typically about a fourth of what is in a standard painkiller tablet, so the effects on the body may be quite different than those of a larger dose. (And note that any aspirin use during pregnancy should be under the guidance of a physician.) However, a study published in 2014 found that aspirin does not prevent pregnancy loss and should not be used for this purpose.

What Is Aspirin?

Aspirin is an NSAID anti-inflammatory medication. Prescription-strength aspirin is given to relieve the pain of rheumatoid arthritis, osteoarthritis and other rheumatologic conditions. Nonprescription aspirin, or aspirin that can be purchased over the counter, is used to treat daily aches and pains, such as headache. Nonprescription aspirin can also be used to treat fever. Furthermore, aspirin is also prescribed to people with heart disease to prevent future heart attack. Aspirin is also used to prevent stroke.

Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) work by inhibiting the action of the enzyme cyclooxygenase. Cyclooxygenase triggers the formation of prostaglandins that cause swelling, fever and pain. Thus, aspirin indirectly inhibits the production of prostaglandins and thus helps decrease swelling, fever and pain.

Was this page helpful?
Article Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. De jong PG, Kaandorp S, Di nisio M, Goddijn M, Middeldorp S. Aspirin and/or heparin for women with unexplained recurrent miscarriage with or without inherited thrombophilia. Cochrane Database Syst Rev. 2014;(7):CD004734. doi:10.1002/14651858.CD004734.pub4

  2. Nielsen GL, Sørensen HT, Larsen H, Pedersen L. Risk of adverse birth outcome and miscarriage in pregnant users of non-steroidal anti-inflammatory drugs: population based observational study and case-control study. BMJ. 2001;322(7281):266-70. doi:10.1136/bmj.322.7281.266 

  3. Li DK, Liu L, Odouli R. Exposure to non-steroidal anti-inflammatory drugs during pregnancy and risk of miscarriage: population based cohort study. BMJ. 2003;327(7411):368. doi:10.1136/bmj.327.7411.368

  4. Keim SA, Klebanoff MA. Aspirin use and miscarriage risk. Epidemiology. 2006;17(4):435-9. doi:10.1097/01.ede.0000221693.72971.b3

  5. Babb M, Koren G, Einarson A. Treating pain during pregnancyCan Fam Physician. 2010;56(1):25–27.

  6. James AH, Brancazio LR, Price T. Aspirin and reproductive outcomes. Obstet Gynecol Surv. 2008;63(1):49-57. doi:10.1097/OGX.0b013e31815e8731

  7. Schisterman EF, Silver RM, Lesher LL, et al. Preconception low-dose aspirin and pregnancy outcomes: results from the EAGeR randomised trialThe Lancet. 2014;384(9937):29-36. doi:10.1016/s0140-6736(14)60157-4.

  8. U.S. National Library of Medicine. ToxNet. Acetylsalicylic Acid. Updated May 8, 2008.