Estrogen-based birth control increases your risk of developing blood clots (venous thromboembolism or VTE) by three to four times compared to women not using hormonal contraception.^1,2,3 This elevated risk applies to:

• Combined oral contraceptives (estrogen-based birth control pills)
• Contraceptive patches
• Vaginal rings

Third and fourth generation combined oral contraceptives carry slightly higher VTE risk than second generation pills, though all estrogen-containing methods increase clotting risk compared to non-hormonal options. (4,5)

Understanding your blood clot risk with birth control:

While estrogen-containing contraceptives increase blood clot risk, the risk for healthy young women with no additional risk factors remains low. (4,5) However, this risk varies significantly based on individual health factors and circumstances.

For perspective, pregnancy itself carries a higher blood clot risk than most forms of hormonal birth control and the postpartum period presents the highest risk of all.(7,8)

Pregnancy increases blood clot risk by four to five times compared to non-pregnant women.(9,10,11) This natural adaptation helps protect against hemorrhage during childbirth but creates vulnerability to dangerous clots.

The risk peaks after delivery. During the first six weeks postpartum, new mothers face a 20x higher risk of developing VTE.(12,13,14). Blood clots can occur throughout pregnancy, though deep vein thrombosis appears more frequently in the left leg.

Why pregnancy increases blood clot risk

Several physiological changes contribute to blood clots during pregnancy:

• Slowed blood flow throughout the body
• Compression of major pelvic veins by the expanding uterus.
• Hormone-induced changes that make blood clot more easily

Treatment and prevention

Women with previous blood clots, thrombophilia, or certain medical conditions may need anticoagulation therapy throughout pregnancy and postpartum. Injectable anticoagulants such as low molecular weight heparin (LMWH) don’t cross the placenta and don’t enter breast milk in clinically significant amounts, allowing safe breastfeeding during treatment

All pregnant women should receive VTE risk assessment:

• At the first prenatal visit
• During any hospitalization
• Immediately after delivery

Perimenopause typically begins in a woman’s mid-to-late 40s, bringing fluctuating hormones and symptoms like hot flashes, night sweats and sleep disturbances. (18)

Hormone replacement therapy (HRT) effectively treats these symptoms, but formulation matters for blood clot risk:

• Oral hormone therapy increases VTE risk by approximately two to three times. (19,20,21)
• Transdermal hormone therapy (patches, gels, or sprays) presents much lower risk because it bypasses the liver, where clotting factors are produced.(22,23,24), therefore making it a good option for patients with a history of blood clots.

Special considerations for women at risk

Women with inherited thrombophilias, such as Factor V Leiden or prothrombin gene mutation, may have an increased risk of developing a blood clot with hormone replacement therapy, making it important to speak to a healthcare professional about treatment options. Many patients with a history of blood clots may be candidates for transdermal HRT to help alleviate menopausal symptoms, however this decision requires careful discussion and supervision (25).

Long-term cardiovascular considerations

Women experiencing early menopause (before age 45) face increased stroke risk in later years. (26,27,28) Estrogen protects cardiovascular health during reproductive years; its loss correlates with rising heart and blood vessel risks.