In plain words
Low-molecular-weight heparin is a type of blood thinner. It is usually given as an injection under the skin. It is the standard blood thinner used in pregnancy and after birth when a clot is suspected or confirmed, and for some people at high clot risk. Enoxaparin is a common example. Heparin medicines do not cross the placenta in meaningful amounts, which is one reason they are chosen in pregnancy over some other blood thinners. They can cause bruising at the injection site, and they carry a risk of bleeding. Some people learn to give their own injections. Whether to use this medicine is decided with a provider, based on the risk of clots, bleeding, and other factors. It is not a treatment for every swollen leg. Ask your provider what it is for in your situation.
The deeper version
Low-molecular-weight heparins are fragments of unfractionated heparin that potentiate antithrombin and inhibit factor Xa. They do not cross the placenta in clinically significant amounts and do not cause the warfarin embryopathy, which is why they are the standard anticoagulant in pregnancy. ACOG Practice Bulletin 196 (2018) and RCOG Green-top Guideline 37a (2015) specify LMWH for confirmed or strongly suspected in pregnancy and for prophylaxis in defined high-risk groups. Both recommend against warfarin in pregnancy, and against direct oral anticoagulants. Risks include bleeding, heparin-induced thrombocytopenia, bone density loss with prolonged use, and injection-site reactions. The controversy concerns the duration of postpartum prophylaxis, and the monitoring needed for people with kidney impairment or extremes of body weight.
Where it comes up
- Blood clots: the signs to knowPostpartum: Your Body
- Swelling: feet, ankles, hands, facePregnancy: Your Body
- Swelling after birthPostpartum: Your Body
- Medications and breastfeeding: how to checkFeeding Your Baby
What mothers here say about low-molecular-weight heparin
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Sources
- American College of Obstetricians and Gynecologists — Practice Bulletin No. 196: Thromboembolism in Pregnancy, 2018
- Royal College of Obstetricians and Gynaecologists — Green-top Guideline No. 37a: Prevention of Venous Thromboembolism in Pregnancy and the Puerperium, 2015