How Heparin Helps Prevent Recurrent Miscarriages

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Approximately 1% of women experience recurrent miscarriages, according to the American College of Obstetricians and Gynecologists. While multiple contributing factors may be involved, sadly about 50% to 75% of the time, there is no known cause for recurrent miscarriages. 

For patients with diagnosed underlying health conditions, treatment can be tailored to improve the chance of a successful pregnancy. Here's how the blood thinner heparin can have a striking impact on pregnancy outcomes for certain patients.

Assessing the Cause of Miscarriage

Before choosing a course of action, your doctor will evaluate the potential causes of your repeated miscarriages. This involves reviewing your medical history, discussing prior pregnancies, doing a physical and/or pelvic exam, performing blood tests, and completing karyotype, microarray, and/or imaging tests.

Some known causes of recurrent miscarriages include:

  • Diabetes
  • Polycystic ovary syndrome (an endocrine disorder in which the ovaries are enlarged and contain cysts)
  • Random chromosomal abnormalities
  • Septate uterus (a band of tissue runs down the middle of the uterus and partially or completely divides it)

Roughly 65% of women who have recurrent miscarriages with no known cause will have a successful pregnancy the next time they conceive.

Thrombophilia Disorders

Another possible cause of recurrent miscarriage is a group of medical conditions that increase blood clotting, called thrombophilia disorders. The specific form of thrombophilia that's most often tied to miscarriage is called antiphospholipid syndrome.

With thrombophilia disorders, researchers believe that tiny clots get stuck in the developing placenta, blocking the flow of nutrients to the baby and eventually leading to an early pregnancy loss (or other complications, such as pre-eclampsia). Thrombophilia disorders are also thought to cause other issues with the placenta.

Bloodwork helps identify certain markers to diagnose antiphospholipid syndrome. Other diagnostic criteria for the syndrome include:

  • At least one confirmed instance of thrombosis
  • The loss of a fetus beyond 10 weeks of gestation
  • Placental insufficiency or preeclampsia that results in preterm delivery at 34 weeks or less
  • Three or more early miscarriages (within the first 10 weeks of pregnancy)

Heparin for Miscarriage Prevention

For patients with thrombophilia conditions and recurrent miscarriages, a common course of treatment is the anticoagulant medication heparin. Heparin injections "thin" the blood, decreasing the tendency to form clots. These injections are often provided alongside a low dose of "baby" aspirin

The form of heparin that's preferred during pregnancy is called low molecular weight heparin (LMWH). Compared to other variants, LMWH is better absorbed, lasts longer, and isn't associated with as much bone loss.


Studies on heparin for patients with known antiphospholipid syndrome are encouraging. In one study, women with recurrent pregnancy loss experienced a 71% subsequent live birth rate when treated with heparin and low-dose aspirin, compared to a 42% live birth rate for those given aspirin alone. Another similar trial found that heparin treatment boosted the live birth rate by 50%

Experts have theorized that heparin may prevent recurrent miscarriages even in patients who test negative for antiphospholipid antibodies. They postulated that unexplained miscarriages might be due to an unrecognized blood-clotting disorder. Unfortunately, a 2010 study found that neither heparin nor low-dose aspirin improved birth rates in patients without antiphospholipid antibodies.

Due to the risks and uncertain benefits, heparin treatment is recommended only for those with a confirmed diagnosis of antiphospholipid syndrome or an inherited thrombophilia disorder. If another cause of recurrent miscarriage is identified, your doctor can recommend another treatment that's more specific to your situation.


Using heparin during pregnancy is not without risk. Side effects of heparin treatment may include bleeding and decreased bone density. For individuals with antiphospholipid syndrome, the benefits of heparin usually outweigh the risks. Your doctor can discuss the costs and benefits of taking heparin to help you understand what side effects to look out for and decide whether it's right for you.

A Word From Verywell

The experience of one miscarriage is devastating, let alone recurrent miscarriages. Unfortunately, not knowing the cause of miscarriage makes it difficult to know what to expect if you choose to become pregnant again. Seeking therapy and support can help you manage challenging emotions along your journey.

5 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. American College of Obstetricians and Gynecologists. Repeated miscarriages.

  2. Simcox L, Ormesher L, Tower C, Greer I. Thrombophilia and pregnancy complications. IJMS. 2015;16(12):28418-28428. doi:10.3390/ijms161226104

  3. Battinelli EM, Marshall A, Connors JM. The role of thrombophilia in pregnancy. Thrombosis. 2013;2013:1-9. doi:10.1155/2013/516420

  4. Kaandorp SP, Goddijn M, Van der post JA, et al. Aspirin plus heparin or aspirin alone in women with recurrent miscarriage. N Engl J Med. 2010;362(17):1586-96. doi:10.1056/NEJMoa1000641

  5. U.S. National Library of Medicine, ToxNet. Heparin.

By Krissi Danielsson
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage.