Timing of Pulmonary Embolism Development After Starting Oral Contraceptives
Pulmonary embolism (PE) can develop within the first few months after starting oral contraceptives, with cases documented as early as 4 months after initiation of therapy. 1, 2
Risk Timeline and Factors
- PE risk increases shortly after starting oral contraceptives, with evidence showing cases developing within the first 4 months of use 1, 2
- The increased risk of venous thromboembolism (VTE) is apparent within 4 months of starting oral contraceptives 3
- The risk disappears within 3 months after discontinuing oral contraceptives 3
- The risk is not affected by the duration of current oral contraceptive use 3
Risk Stratification
- Combined oral contraceptives (containing both estrogen and progestogen) are associated with a 2-6 fold increase in VTE risk over baseline 4
- Third-generation combined oral contraceptives (containing progestogens like desogestrel or gestodene) carry a higher VTE risk than second-generation contraceptives (containing levonorgestrel or norgestrel) 4, 3
- The absolute risk remains low in most users, with reporting rates of PE estimated at 1.72 cases per 100,000 treatment years 5
- Fatal PE occurs at a rate of approximately 0.25 cases per 100,000 treatment years 5
Risk Factors for Severe Outcomes
Several factors may increase the risk of fatal outcomes from oral contraceptive-associated PE:
- Age >35 years 5
- Increased body mass index (BMI >25 kg/m²) 3
- Presence of nausea or abdominal pain at presentation 5
- Concomitant use of other medications that increase VTE risk 5
- Vein or lymph vessel malformations 5
- Deep vein thrombosis above the knee level 5
- History of hypertension during pregnancy (particularly in European women) 3
- Severe inherited thrombophilia 4
Clinical Implications
- Hormone-releasing intrauterine devices and some progesterone-only pills (at contraceptive doses) are not associated with significant increases in VTE risk and may be safer alternatives 4
- Women who develop hormone-associated PE or DVT are generally advised to discontinue oral contraceptive use 4
- Anticoagulant therapy for 3 months is typically sufficient for women with hormone-associated VTE if the hormone therapy is stopped at diagnosis 4
- Women should discontinue hormonal therapy before stopping anticoagulant therapy 4
Important Considerations
- Even young, otherwise healthy women with no additional risk factors may develop PE while using low-dose formulations of combined oral contraceptives 2, 6
- The mechanism of oral contraceptive-induced thrombosis may involve hemorheological changes, increased platelet or leukocyte aggregation, direct effects on clotting factors, or immune-mediated vascular damage 6
- Screening for clotting abnormalities may be justified in patients with a family history of thrombosis or past history of recurrent deep venous thrombosis, especially at a young age 6
In summary, while the absolute risk remains low, PE can develop relatively quickly after starting oral contraceptives, with documented cases occurring within the first few months of use. The risk varies based on the type of contraceptive and individual risk factors, and resolves within months after discontinuation.