The Role of Low-Dose Aspirin in Preventing Miscarriages

If you have a blood disorder and are pregnant, your doctor may recommend aspirin

Pills from a bottle
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You may have read that taking a low dose or baby aspirin while pregnant can help lower your risk of miscarriages. However, the theory behind taking low-dose aspirin while pregnancy is a little complicated.

One possible cause of recurrent miscarriages is having a disorder like antiphospholipid syndrome or other thrombophilia, a type of blood disorder which increases the likelihood of blood clots.

If you have a thrombophilia disorder, you have an increased tendency to form blood clots, which, after forming in your blood can potentially 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 thinner 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 able to prevent miscarriages, especially if you have a blood disorder.

What Is Antiphospholipid Syndrome?

Antiphospholipid syndrome is an autoimmune disorder involving the production of antibodies that attack phospholipid-binding proteins instead of phospholipids. Those 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. Women with antiphospholipid syndrome tend to have recurrent miscarriages.

Antiphospholipid syndrome is considered a high-risk obstetrical condition, if you have antiphospholipid syndrome, you should be managed by specialists. This condition is treated with aspirin and heparin.

Researchers aren't sure what exactly causes antiphospholipid syndrome. However, we do know that antiphospholipid syndrome tends to run in families, and is to some extent genetic, and is associated with HLA-DR4, DRw53, DR7 and the C4 null allele.

Thrombophilia Disorders During Pregnancy

Numerous studies have looked at low-dose aspirin in pregnancy, and the consensus is that low-dose aspirin or injections of heparin, another blood thinner, count as 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. Baby aspirin might be beneficial for other pregnancy complications, like growth restriction of the baby or pregnancy-induced high blood pressure, but a conclusion has not been made yet.

Low-dose aspirin is thought to be safe even in pregnancy, so your physician may recommend you try taking low-dose aspirin if you have had recurrent miscarriages.

Even though aspirin is available over the counter, always get your doctor’s approval before taking baby aspirin during pregnancy. Be sure to mention any other medications you may be taking as aspirin can interact with other medications and may be dangerous for people with specific bleeding disorders.


  • National Library of Medicine. "Immunizations and Chemoprophylaxis." HSTAT: Guide to Clinical Preventive Services: Second Edition
  • 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.