Doctor, I finished 3 months of blood thinners after a blood clot caused by birth control pills. What is my risk of another blood clot if I stop birth control pills and my blood thinner now?

After finishing at least 3 months of blood thinner treatment, some women with a history of blood clots caused by birth control pills (called combined oral contraceptives [COCs]) may be able to safely stop blood thinners if they also stop COCs.

Notes: The longer a woman was taking COCs prior to being diagnosed with a blood clot (for example, 6 months or longer), the higher the chance that COCs were not the only reason for her blood clot. Always talk to your doctor before stopping medications.

These results do not apply to women who continue or restart taking COCs after stopping blood thinner treatment.

Study highlights

Women whose first blood clot was caused by COCs who stopped taking COCs after finishing at least 3 months of blood thinner treatment had about one-third of the risk, or a 66% lower chance, of getting another clot compared to women with a blood clot without risk factors (unprovoked) who stopped blood thinners.

What's the issue?

Birth control pills containing both estrogen and progesterone (COCs) increase the risk of blood clots. For women who had a blood clot while taking COCs and have completed at least 3 months of blood thinner treatment, it is unclear if it is safe for them to stop blood thinners if they also stop COCs.

Staying on long-term anticoagulants reduces the risk of having another DVT or PE, but it also increases the risk of bleeding.

The researchers wanted to understand the risk of another blood clot in women who stopped COCs after completing blood thinner treatment (at least 3 months). This information may help with the decision about how long women with blood clots caused by COCs should be treated with blood thinners. They used a statistical method called a meta-analysis to answer this question.

The meta-analysis compared the risk of developing another blood clot in women with a COC-associated blood clots to women with blood clots without risk factors (unprovoked).

The research

This review looked at 19 studies and included two groups of women who had stopped taking blood thinners after a minimum of 3 months of treatment:

Who?

COC-associated blood clot group: 1,537 women who developed a blood clot while taking COC and stopped taking them.
Unprovoked blood clot group: 1,974 women who developed a blood clot without a clear cause (unprovoked).

What? The studies compared the risk of getting another clot between these two groups after finishing treatment with blood thinners.

Summary of findings

Risk of developing another blood clot in women after completing at least 3 months of blood thinner treatment:

Patient Group	Rate of recurrent VTE per 100-person years	Effect in women who stopped both COCs and blood thinners
Women with COC-associated blood clots	1	If 100 women with COC-associated blood clots were followed for 1 year, about 1 of them would develop a new blood clot
Women with unprovoked blood clots	4	If 100 women with unprovoked blood clots were followed for 1 year, about 4 of them would develop a new blood clot

Patient Group

Rate of recurrent VTE

per 100-person years

Effect in women who stopped both COCs and blood thinners

Women with COC-associated blood clots

If 100 women with COC-associated blood clots were followed for 1 year, about 1 of them would develop a new blood clot

Women with unprovoked blood clots

If 100 women with unprovoked blood clots were followed for 1 year, about 4 of them would develop a new blood clot

This risk was statistically significant, meaning that the results of the study are unlikely to have happened by chance. It suggests that there is a real difference or relationship between the factors being studied.

This Evidence Summary is based on the following article:

Abdulrehman J, Elbaz C, Aziz D, et al. Recurrence after stopping anticoagulants in women with combined oral contraceptive-associated venous thromboembolism: A systematic review and meta-analysis. Br J Haematol. 2022 Oct;199(1):130-142. doi: 10.1111/bjh.18331. Epub 2022 Jul 25. PubMed

Author Details

Karla Machlab, MD

Karla Machlab is an internal medicine resident and incoming hematology fellow at the University of Toronto. With a passion for medical education and health advocacy, she is dedicated to providing accessible and patient-centered care.

Author Details

Zachary Liederman, MD

Zach recently graduated from the University of Toronto Hematology Residency Program and is currently pursuing additional training as both a CanVECTOR fellow and as the Alexandra Yeo Fellow in Thrombosis and Hemostasis at the University of Toronto. He is in the process of completing a Master’s degree in medical education and looks forward to contributing to existing and new teaching projects centered around thromboembolism.

Published: Thursday, November 28, 2024

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.

This Evidence Summary was printed from the CLOT+ website on 2025/03/13.

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