Pregnancy Is Prevented When the Body Is Tricked into Thinking It’s Pregnant

Most birth control pills contain the hormones estrogen and synthetic progesterone, called progestin, and contribute to an increased risk of blood clots, because they cause the level of clotting factors or clotting proteins in a woman’s body to increase.

The pill, the patch or the ring — when they contain estrogen — all do the same thing: They cause the body to hormonally imitate pregnancy, or to think it’s pregnant. In doing so, they prevent pregnancy.

Women’s bodies have evolved over time to offer them some protection from serious bleeding related to pregnancy. Their bodies actually produce more clotting factor proteins, very early on in the pregnancy, so that their blood will clot more readily and protect them from any bleeding challenge that might occur with a miscarriage or during childbirth.

When birth control methods made with pregnancy hormones like estrogen and progestin cause the body to think that it’s pregnant, these same changes will occur, putting women at an increased risk for blood clots.

The most common method of birth control in the United States is the birth control pill, also known as an oral contraceptive. While the absolute risk for a blood clot for the average woman taking birth control pills might be considered relatively low – about 1 in 3000 – the risk is much more significant for a woman who has a clotting disorder, a family history of blood clots, or who previously experienced a blood clot.

Some of the newer birth control pills available to women actually pose a greater blood clot risk than the older oral contraceptives.

Similarly, the use of birth control patches and rings pose an even greater blood clot risk, because the amount of estrogen absorbed from the patches is reported to be 60 percent higher than the amount of estrogen delivered by pills.

Birth Control Methods and Blood Clot Risks

What’s Your Risk?

The birth control pill, the patch and the ring do not directly cause blood clots, but they do increase the risk that a woman might experience a blood clot.

The use of birth control pills with estrogen increases a woman’s risk for blood clots three-fold, and some of the newer birth control pills women use are now recognized to pose a risk two-times greater than older birth control pills.

The use of patches and rings containing estrogen poses a risk double that of birth control pills.

Injectable progestin (DMPA) may increase blood clotting risk up to two-fold.

The risk of blood clots with estrogen-containing birth control methods is much higher in women who have a history of blood clots or who have an inherited or acquired clotting disorder, unless they are taking anticoagulation therapy or blood thinners.

How Can You Reduce Your Risk?

Whether you have a clotting disorder or not, you can plan your family as you choose. There are safe alternatives if you want to avoid the increased risk of blood clots associated with birth control methods that contain estrogen. Several of these options include:

Barrier methods


Progestin implant

Copper IUD

Progestin IUD

Progestin-only pills, which studies show do not increase the risk for blood clots

Tubal ligation or vasectomy for their partner

Prevent Blood Clots

 Know the Signs and Symptoms, Be Your Own Advocate

Understand the symptoms of blood clots and pay attention to your body for signs of a problem.

Symptoms of blood clots in the deep veins of the legs or arms, where they commonly form, include pain and swelling, with skin that might be discolored and/or warm to the touch.

The symptoms of blood clots in the lungs include chest pain, particularly with a deep breath, coughing up blood, and an accelerated heart rate.

Work with your doctor to choose the safest and most effective contraceptive method for you.

Talk to your doctor about blood clotting risks before taking an estrogen-based birth control method, or even if you already use this type of birth control, since different types of birth control pose different risks.

Talk to your relatives about your potential family history of blood clots.

Do you have a history of blood clots or an inherited or acquired blood clotting disorder?

There’s more information you may need: 

Women who are already taking anticoagulation therapy, or blood thinners, may take birth control pills with estrogen. However anticoagulation may make women vulnerable to heavy menstrual bleeding or bleeding at the time of ovulation each month. Heavy menstrual bleeding can be managed and is not a reason to discontinue anticoagulants. Talk to your doctor about options for managing heavy menstrual bleeding while taking anticoagulants.

For More Information About Blood Clots, Visit:

The National Blood Clot Alliance

The information and materials on this site are provided for general information purposes only. You should not rely on the information provided as a substitute for actual professional medical advice, care, or treatment. This site is not designed to and does not provide medical advice, professional diagnosis, opinion, treatment, or services to you or any individual. If you believe you have a medical emergency, call 911 immediately.

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