Understanding Blood Clot Risk and Hormonal Birth Control
Hormonal birth control, especially methods containing estrogen, increases a person's risk of developing venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). This occurs because estrogen affects the body's clotting factors, promoting coagulation. The risk, however, is a relative increase over a very low baseline. The risk of a blood clot during pregnancy and the postpartum period is significantly higher than with most birth control pills.
Not all hormonal contraceptives carry the same risk. The level of risk is influenced by the type and dose of the hormones used, particularly the type of progestin and the amount of estrogen in a combined oral contraceptive (COC).
Progestin-Only Pills (POPs): The Lowest Risk Option
Progestin-only pills (POPs), also known as "mini-pills," are generally the safest hormonal option for those seeking the lowest possible risk of blood clots. They contain no estrogen. Studies indicate that progestin-only methods do not appear to increase the risk of blood clots in healthy women.
- How They Work: POPs use progestin to thicken cervical mucus and prevent sperm from reaching the egg. They may not consistently inhibit ovulation and require strict timing for effectiveness.
- Candidate Users: POPs are suitable for women with higher VTE risk factors like age, smoking, a history of blood clots, or genetic predispositions.
- Other Progestin-Only Options: Other low or no-risk progestin-only methods include hormonal IUDs (Mirena, Kyleena) and contraceptive implants (Nexplanon).
Second-Generation Combined Pills: Lower Risk Among Combined Options
Among combined oral contraceptives (COCs), second-generation pills are associated with a lower blood clot risk compared to third- and fourth-generation formulations.
- Key Hormones: These pills combine low-dose estrogen (ethinyl estradiol) with a second-generation progestin like levonorgestrel or norethisterone.
- Why They Are Safer (Relatively): Research shows that COCs containing levonorgestrel and low-dose estrogen have the lowest VTE risk among combined pills. This is due to the specific progestin and lower estrogen dose having less impact on clotting factors.
- Examples: Brands include Rigevidon, Microgynon 30, Levest, and Ovranette.
Higher-Risk Pill Formulations
Newer COCs with different progestins or higher estrogen doses have been linked to a higher risk of VTE.
- Third-Generation Progestins: These include desogestrel and gestodene, which are associated with a higher blood clot risk than levonorgestrel-based pills.
- Fourth-Generation Progestins: Drospirenone (in brands like Yaz, Yasmin) may carry a higher risk compared to other pills, according to some studies and FDA warnings.
- High-Dose Estrogen: Pills with higher estrogen doses (e.g., 50 mcg) have a greater VTE risk. Modern pills typically use lower doses (20-35 mcg).
Comparison of Birth Control Pills and Blood Clot Risk
| Pill Type | Key Hormones | Relative VTE Risk | Example Brands |
|---|---|---|---|
| Progestin-Only | Progestin (e.g., norethindrone) | None or very little increased risk compared to non-users | Camila, Nora-Be, Jolivette |
| Second-Generation Combined | Low-dose estrogen + Levonorgestrel or Norethisterone | Lowest risk among combined pills; increased 3-4 times over non-users | Rigevidon, Microgynon 30, Levlen ED |
| Third-Generation Combined | Estrogen + Desogestrel or Gestodene | Higher risk than second-generation; increased 6-8 times over non-users | Ortho-Cept, Desogen, Marvelon |
| Fourth-Generation Combined | Estrogen + Drospirenone | Evidence of potentially higher risk than second-generation | Yasmin, Yaz, Ocella |
Factors That Influence Your Risk
Personal health factors also influence VTE risk with hormonal birth control:
- Smoking: Contraindicates COCs in women over 35 due to substantially increased cardiovascular risks.
- Age: Risk increases with age, higher after 40.
- Obesity: BMI over 30 is a risk factor magnified by COCs.
- Personal or Family History: Past VTE or family history of clotting disorders increases risk, often requiring non-estrogen options.
- Prolonged Immobilization: Periods of immobility from surgery or travel increase VTE risk and may require stopping hormonal birth control temporarily.
The Importance of Consultation
Choosing the safest birth control method requires consulting a healthcare provider. They assess your medical history, including blood clot history, smoking, and other risk factors, to recommend the best option. If hormonal options are too risky, non-hormonal methods like the copper IUD or barrier methods are alternatives. Blood clot risk typically returns to baseline weeks after stopping hormonal contraception.
Conclusion: Making an Informed Choice
Progestin-only pills offer the lowest blood clot risk among hormonal options. If a combined pill is preferred, second-generation formulations with levonorgestrel and low-dose estrogen have the lowest risk among COCs. Newer pills with desogestrel, gestodene, or drospirenone, and higher estrogen doses, carry a higher risk. While the absolute risk is low for most, understanding these differences and discussing personal factors with a healthcare provider is vital for safe and effective contraception. The American Society of Hematology offers additional insights into managing blood clot risk and contraception.
