Can Low-Dose Aspirin Prevent Miscarriages?

Low-Dose Aspirin Could Help Pregnant Women With Thrombophilia

Pregnant woman taking vitamins
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If you have started researching miscarriage treatment and prevention, you may have seen references to the idea of taking low-dose or “baby” aspirin to treat recurrent miscarriages. But does this treatment really work? And if aspirin prevents miscarriages, why do they tell you to never take aspirin when you’re pregnant?

Can Low-Dose Aspirin Prevent Miscarriages?

The theory behind using low-dose aspirin in pregnancy is a little complicated.

One possible cause of recurrent miscarriages is having a disorder like antiphospholipid syndrome (or other thrombophilia). Having a thrombophilia disorder means an increased tendency to form blood clots, and researchers theorize that tiny clots form in the blood and get stuck in the tiny blood vessels of the placenta, possibly cutting off the supply of nutrients to the baby.

Aspirin acts as a blood thinner, and thinned blood is less likely to clot. Higher doses of aspirin (such as the tablets that you might take when you have a headache) can cause complications in pregnancy, but researchers have been experimenting with lower dose aspirin or baby aspirin to see whether it might be beneficial to prevent miscarriages.

So far, numerous studies have looked at low-dose aspirin in pregnancy, and right now the consensus is that low-dose aspirin or injections of heparin (another blood thinner) is a good therapy for women with diagnosed thrombophilia disorders.

The jury is still out on whether taking low-dose aspirin might benefit women who have had recurrent miscarriages but do not have a diagnosed thrombophilia disorder. Some studies have examined this notion and found no benefit to taking low-dose aspirin while other studies have found possible benefit, and still other studies are still ongoing.

Some studies are also investigating whether baby aspirin might be beneficial for other pregnancy complications, like growth restriction of the baby or pregnancy-induced high blood pressure, but the verdicts are not yet in.​

Low-dose aspirin is thought to be safe even in pregnancy, so some physician will recommend that women with recurrent miscarriages should try taking low-dose aspirin with the idea that it “can’t hurt, and might help.” Even though aspirin is available over the counter, be sure to try using baby aspirin in pregnancy only with a doctor’s approval. Aspirin can interact with other medications and also might be dangerous for people with specific bleeding disorders.

What Is Antiphospholipid Syndrome?

Antiphospholipid syndrome is an autoimmune disorder involving the production of antibodies that attack phospholipid-binding proteins instead of phospholipids. Consequently, people with antiphospholipid syndrome develop thrombophilia and clot much more easily. This increased tendency to clot can cause vascular thrombosis and pregnancy complications as well as deep vein thromboses which can lead to a life-threatening pulmonary embolism. Furthermore, women with antiphospholipid syndrome tend to have recurrent miscarriages.

Antiphospholipid syndrome is a high-risk obstetrical condition which is managed by specialists. This condition is treated with aspirin and heparin.

Although we know that antiphospholipid syndrome is autoimmune in nature, we don't know exactly what causes it. We also know that antiphospholipid syndrome runs in families, and is to some extent genetic. Specifically, this condition is associated with HLA-DR4, DRw53, DR7 and the C4 null allele.


National Library of Medicine. "Immunizations and Chemoprophylaxis." HSTAT: Guide to Clinical Preventive Services: Second Edition. 1996. Accessed 11 Dec 2007.

Rai, R., H. Cohen, M Dave, and L. Regan. "Randomised controlled trial of aspirin and aspirin plus heparin in pregnant women with recurrent miscarriage associated with phospholipid antibodies (or antiphospholipid antibodies)." British Medical Journal 25 Jan 1997: 253-257. Accessed 11 Dec 2007.


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