How Heparin Helps Prevent Recurrent Miscarriages

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Approximately 1 percent of women will experience recurrent miscarriages (defined as two or more miscarriages), according to the American Congress of Obstetricians and Gynecologists. They can occur due to a number of causes. Some causes are more understood than others, and 50 percent to 75 percent of the time, there is no known cause for recurrent miscarriages. 

To try to understand what may be causing your recurrent miscarriages, a doctor might ask you questions about your medical history and prior pregnancies, perform a physical and/or pelvic exam, give you blood tests, do a karyotype and microarray testing, and/or do imaging tests. The good news is that roughly 65 percent of women who have recurrent miscarriages with no known cause will have a successful pregnancy the next time they conceive.

Causes of Recurrent Miscarriages

Some known causes of recurrent miscarriages include random chromosomal abnormalities, a septate uterus (that's when a band of tissue runs down the middle of the uterus and either partially or completely separates it), diabetes, and polycystic ovary syndrome (an endocrine disorder in which the ovaries are enlarged and contain fluid).

Other possible causes are thrombophilia disorders, medical conditions in which the blood has an increased tendency to clot. The thrombophilia disorder that is most clearly tied to miscarriages is called antiphospholipid syndrome.

Why Thrombophilia Disorders Are Linked to Miscarriage

In thrombophilia disorders, researchers believe that tiny clots get stuck in the developing placenta, blocking the flow of nutrients to the baby and eventually causing miscarriage (or increasing the risk of other pregnancy complications, such as pre-eclampsia). It's also been theorized that thrombophilia disorders might cause other problems with the placenta.

How Thrombophilia Disorders Are Treated in Pregnant Women

For women who are diagnosed with thrombophilia conditions and recurrent miscarriages, a common treatment is heparin, often alongside low-dose "baby" aspirin. Heparin injections are known as anti-coagulants that thin the blood and decrease its tendency to form clots. Evidence from 2005 suggests that heparin treatment during pregnancy reduces miscarriage rates for women who have antiphospholipid syndrome and possibly benefits women who have inherited thrombophilia disorders, such as Factor V Leiden mutations. This heparin and low-dose aspirin combination may be prescribed during pregnancy and even for several weeks after delivery.

Is It Safe to Take Heparin?

It should be noted that using heparin during pregnancy is not without risk. The drug can have side effects in some people and may increase the risk of bone loss or the tendency to hemorrhage. But for women with antiphospholipid syndrome, the benefits likely outweigh the risks. It's important to talk to your doctor, of course, before taking any type of drug.

Which Types of Pregnant Women Benefit Most From Heparin?

Some experts had theorized that heparin might be beneficial for women who have recurrent miscarriages and negative tests for antiphospholipid antibodies, postulating that unexplained recurrent miscarriages could be due to some unrecognized blood-clotting disorder, but a 2010 study found that neither heparin nor low-dose aspirin improved birth rates for these women when compared with a placebo.

Therefore, heparin treatment is usually recommended only for women who have both a history of miscarriages and a confirmed diagnosis of antiphospholipid syndrome or an inherited thrombophilia disorder.

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  2. Battinelli EM, Marshall A, Connors JM. The Role of Thrombophilia in PregnancyThrombosis. 2013;2013:1-9. doi:10.1155/2013/516420.

  3. Simcox LE, Ormesher L, Tower C, Greer IA. Thrombophilia and Pregnancy ComplicationsInt J Mol Sci. 2015;16(12):28418–28428. Published 2015 Nov 30. doi:10.3390/ijms161226104

  4. Empson M, Lassere M, Craig J, Scott J. Prevention of recurrent miscarriage for women with antiphospholipid antibody or lupus anticoagulant. Cochrane Database Syst Rev. 2005;(2):CD002859. doi:10.1002/14651858.CD002859.pub2

  5. U.S. National Library of Medicine, ToxNet. Heparin. Updated June 16, 2011.

  6. 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

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