Understanding Desogestrel
Desogestrel is a synthetic hormone known as a progestin, used widely in contraception. It is a third-generation progestin, introduced to offer potentially improved side-effect profiles, such as fewer androgenic effects like acne and unwanted hair growth, compared to older versions. Desogestrel can be found in two main types of hormonal birth control:
- Combined Oral Contraceptives (COCs): These pills contain both estrogen and desogestrel. The presence of both hormones, particularly estrogen, has a significant impact on blood clotting factors.
- Progestin-Only Pills (POPs): Also known as the mini-pill, these pills contain only desogestrel. Unlike COCs, POPs are not associated with an increased risk of blood clots.
Risk Profile of Desogestrel in Combined Oral Contraceptives
Multiple large-scale studies have investigated the risk of venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), in users of different oral contraceptive formulations. Research has consistently shown that users of combined pills containing desogestrel have a higher relative risk of VTE compared to users of second-generation combined pills containing progestins like levonorgestrel.
For example, studies have found that desogestrel-containing COCs confer a risk of VTE that is approximately 1.5 to 2.0 times higher than that of levonorgestrel-containing COCs. When compared to women not using hormonal contraceptives at all, the relative risk is even greater. A Danish study noted that current users of desogestrel COCs had a six- to sevenfold increased risk compared to non-users, whereas levonorgestrel COC users had a threefold increased risk.
Despite this higher relative risk, it is crucial to understand that the overall absolute risk of a blood clot remains low. For perspective, a large UK study found that for every 10,000 women using desogestrel-containing COCs, an estimated 14 additional cases of VTE would be diagnosed annually, compared to 8 additional cases for users of levonorgestrel. For context, the risk of blood clots during pregnancy is much higher—roughly tenfold higher than in non-pregnant women—and far surpasses the risk associated with any type of oral contraceptive.
The reason for the different risk profiles is linked to the specific effects of the progestin on blood clotting. Some studies suggest that third-generation progestins, including desogestrel, may cause an acquired resistance to activated protein C, a natural anticoagulant, thus increasing the blood's tendency to clot.
Desogestrel in Progestin-Only Pills
In contrast to combined pills, the progestin-only pill (POP), which contains only desogestrel and no estrogen, is considered much safer concerning blood clot risk. Studies have found no significant increase in the risk of VTE for users of desogestrel-only pills compared to non-users. This is a critical distinction and explains why progestin-only options are often recommended for individuals who are at a higher risk of developing blood clots but still require hormonal contraception. For instance, women with a history of VTE are often advised to use progestin-only methods.
Comparison of Progestins and Blood Clot Risk
| Progestin Generation | Examples | Relative VTE Risk vs. Non-Users (approximate) | Relative VTE Risk vs. Levonorgestrel (approximate) |
|---|---|---|---|
| Second-Generation | Levonorgestrel, Norethisterone | Threefold | Reference level |
| Third-Generation | Desogestrel, Gestodene | Six to sevenfold | Twofold |
| Fourth-Generation | Drospirenone | Six to sevenfold | Twofold |
Factors Influencing Blood Clot Risk
While the type of progestin in combined pills is a factor, many other elements contribute to an individual's overall risk of developing a blood clot. Understanding these is essential for making an informed decision with a healthcare provider. These factors include:
- Estrogen Dose: The amount of estrogen in a combined oral contraceptive has a dose-dependent effect on VTE risk, with higher doses carrying greater risk. Modern low-dose pills have significantly lower risks than older, high-dose formulations.
- Genetic Predisposition: Some people have inherited conditions, known as thrombophilias, that increase their susceptibility to blood clots. A family history of blood clots is a significant risk factor.
- Obesity: A high Body Mass Index (BMI) is a well-established risk factor for VTE.
- Smoking: Cigarette smoking, especially in women over 35, substantially increases the risk of blood clots and is a strong contraindication for combined oral contraceptives.
- Age: The risk of VTE increases with age, particularly in women over 35.
- Prolonged Immobility: Long periods of sitting, such as during long-distance travel, or bedrest after surgery or injury, can slow blood flow and increase the likelihood of clot formation.
Medical Consultation and Informed Choice
Given the variability in risk profiles, the choice of contraception should always be a personal decision made in consultation with a healthcare provider. A doctor will evaluate an individual's complete medical history, including any personal or family history of blood clots, smoking habits, and other risk factors, to recommend the most suitable option.
For some patients, the non-contraceptive benefits of certain hormonal pills, such as reduced acne or improved menstrual bleeding, may outweigh the small, increased risk of VTE associated with desogestrel-containing combined pills. However, for those with existing risk factors, a second-generation pill with a lower risk or a progestin-only pill may be the safer choice. For many women, progestin-only pills offer effective contraception without increasing the risk of blood clots, making them an excellent alternative.
Conclusion
While desogestrel in combined oral contraceptives is associated with a higher relative risk of blood clots compared to older progestins like levonorgestrel, the overall absolute risk remains low. Critically, progestin-only pills containing desogestrel are not linked to this increased risk. The risk associated with combined pills is also lower than the risk during pregnancy. The decision to use any hormonal contraceptive, including those with desogestrel, requires a thorough assessment of individual health factors by a qualified medical professional. An open discussion with a doctor is the best way to weigh the benefits of contraception against the potential risks and choose the safest option.
- Learn more about contraceptive options and risks from the American Society for Reproductive Medicine: https://www.asrm.org/practice-guidance/practice-committee-documents/combined-hormonal-contraception-and-the-risk-of-venous-thromboembolism-a-guideline-2016/
