Discontinuing birth control pills reduces risk of blood clots

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A Swiss study has found that the risk of blood clots largely disappears within two to four weeks of stopping use of these contraceptives.  

This content was published on November 9, 2023 – 14:24

November 9, 2023 – 14:24

The use of the pill and other combined hormonal contraceptives (CHC) triples the risk of blood clots. The study shows that this risk largely disappears within two to four weeks of stopping use of these contraceptives. This finding is of particular relevance to women who use CHCs and who have to undergo surgery. For example, if they are immobilised for a long period due to surgery the risk of thrombosis increases, according to a joint press release issued on Thursday by the University Hospitals and the University of Geneva (HUG/UNIGE).

+ Fifty years of contraception

The results of this study, published in the journal Blood, are the first to provide indications on the best time to stop CHC before events likely to increase the risk of dangerous clots. The scientists believe that stopping contraceptives two to four weeks in advance should suffice in most of these cases.

The results are also important for guiding the management of CHC after an event such as venous thrombosis or pulmonary embolism. Rather than stopping at the time of diagnosis, CHC could be continued temporarily and stopped four weeks before the end of anticoagulant treatment for thrombosis, in order to reduce the risk of unintended pregnancy and uterine bleeding linked to anticoagulants.

Normalisation in twelve weeks

The study focused on CHCs, in particular oestroprogestogenic contraceptive pills, vaginal rings and transcutaneous contraceptive patches, the most common methods in Europe and North America.

For the study, the team led by Marc Blondon, Associate Physician at the HUG and Senior Lecturer in the Faculty of Medicine at the UNIGE, took blood samples from 66 women using hormonal contraceptives at six different times, before and after stopping their contraception.

The scientists then compared the samples with blood from a control group of 28 women who were not using combined hormonal contraceptives, and measured several biomarkers associated with CHC and coagulation activity. These markers fell rapidly in a week or two following cessation of CHC and, by week 12, had reached the same level as in the control group.

Around 80% of the total fall in coagulation markers observed in these women occurred within two weeks of stopping contraception, and 85% of this fall occurred within four weeks.

In Switzerland, the annual incidence of venous thromboembolic disease, including venous thrombosis and pulmonary embolism, is one to two women aged 15 to 34 in 10,000 and three to five women aged 35 to 44 in 10,000. With the use of CHC, this incidence is three to five times higher for all age categories.

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