The hormone estrogen can raise the risk of developing blood clots. Changes in estrogen levels can come from some types of birth control, pregnancy or hormone replacement therapy (HRT). Thrombosis (clotting) risk rises further with clotting disorders, a family history of clots, or a general tendency to clot more than you should.
If you’re facing a particularly high risk for clots, reach out to the Center for Women’s Thrombosis and Hemostasis. Our specialized Penn Medicine team offers leading blood clotting disorders evaluation and treatment to protect your health in a variety of situations. We can help you safely manage contraception or pregnancy. We can also help anyone undergoing HRT or gender-affirming hormone therapy (GHT).
Birth Control and Blood Clot Risk
Some forms of birth control release estrogen to make your body think you’re carrying a baby and prevent an actual pregnancy. This extra estrogen triggers the production of proteins that promote blood clotting.
In pregnancy, these clotting factors serve as protection against bleeding during a miscarriage or childbirth. With hormonal contraception, the clotting factors introduce some blood clot risk. The risk depends on the amount of estrogen the body absorbs.
For most, the clot risk rises only a little with hormonal birth control, and they can safely use these options. For people with a clotting disorder or a history of clots, the decision to use hormonal birth control can be more complicated. It’s important to get the right information and know your options, since clot risk is actually higher from pregnancy.
At our program, a hematologist works closely with Penn Medicine gynecologists to get you answers and provide options. We can help if you’ve been told your birth control caused a clot or if you have an especially high blood clot risk. We work to find the safest, most effective form of birth control for you. We can also discuss the use of blood thinners to prevent future clots.
Pregnancy and Blood Clot Risk
Estrogen rises throughout pregnancy, peaking in the last trimester. This increase prevents excessive bleeding that could threaten a pregnancy. However, it also places individuals at greater risk for blood clots during pregnancy and for several months after delivery.
The risk goes up further if you:
- Have a C-section delivery
- Can’t be active during pregnancy or after delivery for medical reasons
- Have certain medical conditions, such as diabetes or preeclampsia
Clotting risk rises even higher if you have a clotting disorder or other history of clotting. While all doctors involved with pregnancy care can discuss clots, our specialists can step in when risk is particularly high. We work closely with Penn Medicine specialists in High-Risk Pregnancy Care.
Together, we can discuss possible blood thinner use or what to do if you’re already taking medications for a clotting disorder.
Blood Clots from Hormone-Replacement Therapy or Gender-Affirming Hormone Therapy
The chance of developing blood clots goes up when taking estrogen for menopause or for gender transition. The risk remains modest for most people, but like other estrogen-related risk, it rises more with clotting disorders or a history of clotting.
If you are taking hormone-replacement therapy (HRT), we can assess your risk and discuss blood thinners if you’re not already taking them. We can also work with our Penn Medicine partners to explore alternatives for relieving menopausal symptoms, if needed. That same care and teamwork extends to people who are trying to transition and already face a higher clotting risk before taking estrogen.
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