Thrombophilia & miscarriage: when it matters
Many women with recurrent miscarriage are told they should be tested for “thrombophilia” — a tendency of the blood to clot more easily — and are often offered blood thinners such as heparin or aspirin. Yet the picture painted by current evidence is far more limited, and far clearer, than is often heard.
The essential thing is to separate two entirely different conditions: inherited thrombophilia, which in practice does not appear to increase miscarriage or to respond to blood thinners, and antiphospholipid syndrome, an autoimmune disorder that is the one genuine exception.
What is thrombophilia?
Thrombophilia is an increased tendency of the blood to form clots. It falls into two broad categories. Inherited thrombophilia is caused by genes that are passed down (e.g. factor V Leiden mutation, prothrombin mutation, deficiency of protein C, protein S or antithrombin).
Acquired thrombophilia, whose main form is antiphospholipid syndrome, is autoimmune: the immune system produces antibodies that favour clotting. These two conditions are entirely different in their relationship to miscarriage and in how they are managed.
Does inherited thrombophilia cause recurrent miscarriage?
The older hypothesis was that tiny clots in the placental circulation harm the pregnancy. Modern data, however, do not support a strong link between inherited thrombophilia and recurrent miscarriage.
Do heparin and aspirin help in inherited thrombophilia?
No. This is the most important and most recent finding. The large randomized ALIFE2 trial, published in 2023, studied women with recurrent miscarriage and confirmed inherited thrombophilia and showed no difference in the live-birth rate with low-molecular-weight heparin compared with standard surveillance.
On this basis, neither anticoagulant treatment nor the corresponding testing is recommended in women with miscarriage and inherited thrombophilia for the sole purpose of improving the pregnancy. Heparin has a place when there is an indication to prevent thrombosis — not as a treatment for miscarriage.
What is the exception? Antiphospholipid syndrome
Antiphospholipid syndrome (APS) is the one documented exception. It is an autoimmune, acquired disorder that is genuinely linked to miscarriage and to other pregnancy complications, as well as to thrombosis.
Unlike inherited thrombophilia, here testing is recommended in women with recurrent miscarriage, and there is an effective treatment.
How is antiphospholipid syndrome diagnosed and treated?
Diagnosis requires a combination of clinical history (e.g. recurrent miscarriage) and positive laboratory tests for antiphospholipid antibodies — lupus anticoagulant, anticardiolipin and anti-β2-glycoprotein I antibodies. Crucially, the antibodies must remain positive on repeat testing after at least 12 weeks, to exclude a transient value.
Treatment, according to ESHRE, is the combination of low-dose aspirin with prophylactic-dose heparin. This combination has been shown to increase the live-birth rate in women who meet the criteria for the syndrome — a substantially different picture from inherited thrombophilia.
What about MTHFR testing?
Testing for variants of the MTHFR gene is still often requested in the context of miscarriage, but it is not recommended. These variants are very common in the general population and have not been shown to cause miscarriage.
The useful, simple recommendation for every woman planning a pregnancy remains taking folic acid — independent of any genetic test.
Summary
In inherited thrombophilia, current data do not support a strong link with recurrent miscarriage, and the ALIFE2 trial (2023) showed that heparin does not increase births; ESHRE therefore recommends neither routine testing nor blood thinners for this purpose. The one genuine exception is antiphospholipid syndrome, an autoimmune disorder that is tested for and treated with low-dose aspirin and heparin. MTHFR testing has no role. The right approach is targeted, not a “sweeping” thrombophilia screen for everyone.
Sources: ESHRE, “Recurrent pregnancy loss: an update in 2022” (guideline); ALIFE2 randomized controlled trial (heparin in inherited thrombophilia), The Lancet 2023.
⚕ Medically reviewed by Prof. Stratis Kolibianakis · Thessaloniki Medical Association Reg. No. 16340
ARTICLE 26 · RECURRENT LOSS & FAILURE
