Which hormonal contraceptives, routes of administration, and regimens are associated with the lowest risk of thrombosis?
Shannon Bates: For my personal practice, again, the data are limited. But with respect to hormonal contraception, if I have a woman whom I consider at a very high risk of developing venous thromboembolism (VTE) – maybe she has had an event before, she has a strong thrombophilia – I want to use a hormonal contraception that is likely not associated with any significant increase in the risk of VTE. Again, that would be the levonorgestrel intrauterine device (IUD), or Mirena IUD, and possibly the minipill, progesterone-only pill.
If you are talking about minimizing the risk of hormonally related VTE in general, there are some data that certain forms of combined oral contraceptive pills might have a slightly lower risk of VTE than other forms, for example, forms that use cyproterone acetate or drospirenone. People are very worried that those may increase the risk of VTE, but what you have to bear in mind is that according to data from the European Medicines Agency and the Food and Drug Administration, in absolute terms the difference in risk is very small. So lower-risk combined oral contraceptives might have an annual risk of VTE between 5 to 7 per 10 000 patients per year, whereas the ones that we think of as higher risk might be 9 to 12 per 10 000 patients per year. By switching from one to another, you are not making a very big difference, and in no way can you guarantee to your patients that they are not going to develop VTE. So you can say to them that you are going to use a form that you think is lower risk, but they still have to be willing to accept some risk of VTE to take a combined oral contraceptive, even a lower-risk formulation.