Blood clot risk plummets after stopping hormonal contraception


By Selina Wellbelove

15 Nov 2023

The increased risk of venous thromboembolism from hormonal contraceptives is diminished just two to four weeks after stopping the medication, a small study suggests.

According to the authors of the study published in Blood, the findings could help inform decisions on when patients should stop using contraceptives ahead of surgery or periods of prolonged mobility, or when tapering anticoagulant medicines.

The Swiss researchers analysed blood samples from 66 women on hormone-based birth control across six different time points before and after their use was stopped and compared them with a control group of 28 women who were not using birth control.

The primary outcomes were changes in thrombin generation-based normalised sensitivity ratio to activated protein C (nAPCsr) and thrombomodulin (nTMsr). Pre-specified secondary outcomes were changes in sex hormone-binding globulin (SHBG), protein C, protein S, antithrombin and factor VIII.

The data showed that elevated levels of clotting markers dropped by 80% within one to two weeks after birth control was stopped and by 85% after four weeks. By 12 weeks, the two groups had no significant differences in biomarkers.

“These results were very coherent between 3 different oestrogen-induced biomarkers (resistance to APC, to TM and SHBG), and with raw thrombin generation analyses,” the investigators noted.

“Two-four weeks of cessation of combined hormonal contraceptives appear sufficient to eliminate the accrued associated thrombotic risk,” they concluded.

Looking forward, larger studies are needed to confirm that the study’s findings are generalisable across different populations and whether they translate to a reduction in the risk of actual clotting events, the researchers noted.

Genetics heightens the risk

Meanwhile, a US study based on UK biobank data found that genetics influenced the risk of blood clots in women using hormonal contraceptives.

The research team analysed data from 244,420 British women from the UK Biobank.

Results published in the American Journal of Obstetrics and Gynaecology, showed that those genetically predisposed to venous thromboembolism were six times more likely to develop a blood clot during the first two years of contraceptive pill use.

“This suggests that the polygenic risk score could be used to identify women who are at high risk for developing a venous thromboembolism and advise them on alternative methods of contraception,” the authors noted.

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