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Patient Evidence Summary
Doctor, I am pregnant and had a blood clot in the past. Is a low dose of an injectable blood thinner enough to protect me from another blood clot?
For pregnant women with a history of a previous blood clot, a low dose of injectable blood thinner is just as effective and safe as an intermediate dose of injectable blood thinner for reducing the risk of another blood clot. Please note that this study did not include women who were taking blood thinners long-term or had their previous blood clot in the setting of surgery, trauma, or a leg cast.
Study highlights
Pregnant women (14 weeks gestation or less) with previous venous thromboembolism (VTE) who injected low-dose low molecular weight heparin (LMWH) during pregnancy and for 6 weeks after childbirth, did not have more blood clots than pregnant women who injected an intermediate dose of LMWH.
Understanding the problem
Deep vein thrombosis (DVT) and pulmonary embolism (PE) can be serious and even cause death in pregnant women. Women with a history of VTE have an increased risk of developing new blood clots during pregnancy. To reduce this risk, they are often asked to inject themselves with a blood thinner during pregnancy and for 6 weeks after delivery. Treatment with blood thinners may increase their risk of bleeding and may prevent use of an epidural during labour if taken too close to delivery.
The best dose of LMWH for these pregnant women is not clear. Low-dose LMWH may reduce the risk of bleeding but might not be as effective as intermediate-dose LMWH at reducing the risk of new VTE.
Researchers wanted to know if taking daily injections of intermediate-dose LMWH in pregnant women with a previous episode of VTE, would reduce the risk of new VTE compared to taking low-dose LMWH.
Who? The study included 1,110 pregnant women (recruited when less than 14 weeks pregnant) and who had a previous VTE. Women who had VTE in the setting of surgery, trauma or a leg cast or were taking long-term blood thinners were excluded.
What? The study compared intermediate-dose LMWH with low-dose LMWH. (Intermediate-dose was approximately half of a full-dose based on body weight)
Intermediate-dose LMWH | vs | Low-dose LMWH |
|---|---|---|
Intermediate-dose of LMWH (Fragmin©, Fraxiparin©, Innohep©, Lovenox©) injected under the skin once a day during pregnancy and for 6 weeks after childbirth. The dose was increased as the women gained weight during pregnancy. LMWH stopped at the first signs of labour and at least 24 hours prior to a planned delivery. | Low-dose of LMWH (Fragmin©, Fraxiparin©, Innohep©, Lovenox©) injected under the skin once a day during pregnancy and for 6 weeks after childbirth. This dose was not changed during the pregnancy. LMWH stopped at the first signs of labour and at least 24 hours prior to a planned delivery. |
Intermediate-dose LMWH vs Low-dose LMWH in pregnant women with a history of blood clot
Outcomes at 6 weeks after childbirth | Rate of events with Intermediate-dose LMWH | Rate of events with Low-dose LMWH | Results |
|---|---|---|---|
Venous thromboembolism (VTE) | 2 out of 100 people | 3 out of 100 people | No effect* |
Major bleeding | 4 out of 100 people | 4 out of 100 people | No effect |
*Although the rates for the 2 groups look different, the differences were not statistically significant—this means that the difference could simply be due to chance rather than due to the different treatments.
This Evidence Summary is based on the following article:
Bistervels IM, Buchmuller A, Wiegers HMG, et al. Intermediate-dose versus low-dose low-molecular-weight heparin in pregnant and post-partum women with a history of venous thromboembolism (Highlow study): an open-label, multicentre, randomised, controlled trial. Lancet. 2022 Nov 19;400(10365):1777-1787. doi: 10.1016/S0140-6736(22)02128-6. Epub 2022 Oct 28. PubMed
Amin Zahrai is a MSc Clinical Epidemiology student and CanVECTOR trainee at the University of Ottawa. His research focuses on the prediction and treatment of VTEs using anticoagulants in adult patients with cancer and gastrointestinal diseases. He hopes to incorporate such clinical interests to provide curative treatments in his future trainings.
Lori-Ann Linkins, MD, MSc (Clin Epi), FRCPC
Dr. Linkins is an Associate Professor of Medicine (thrombosis) at McMaster University in Hamilton, Canada. She holds a Masters Degree in Health Research Methodology and is a Deputy Editor with the Health Information Research Unit, McMaster. She is Co-Editor of the ACP Journal Club and Co-lead on the CanVECTOR Knowledge Translation Platform.
Published: Saturday, December 31, 2022
Please note that the information contained herein is not to be interpreted as an alternative to medical advice from a professional healthcare provider. If you have any questions about any medical matter, you should consult your professional healthcare providers, and should never delay seeking medical advice, disregard medical advice or discontinue medication based on information provided here.
, McMaster University