Anyone can be affected by DVT, but certain risk factors based on a person’s sex at birth can raise their risk of developing a DVT. Specifically, estrogen hormonal therapy and hormonal birth control can actually raise a person’s chances developing DVT during childbearing years. “Gender plays an important role in the incidence of venous thromboembolism,” says Gregory Piazza, MD, a cardiovascular medicine specialist at Brigham and Women’s Hospital in Boston and an associate professor of medicine at Harvard Medical School. “From puberty to menopause, women bear the highest risk of venous thromboembolism.” After the menopause years (generally when women are in their fifties), the risk of venous thromboembolism and DVT becomes higher for men — unless hormone replacement therapy is being used. Although it’s not completely clear why there are sex-specific differences in the risk of developing DVT, research has given us some clues.
DVT, Hormone Therapy, and Being Transgender
It’s important to note that very little research has been done on DVT risk in transgender men and women, and most knowledge is based on case studies, which outline an individual patient’s experience rather than how a population is affected. A case study published in April 2017 in the Canadian Medical Association Journal noted that the risk of venous thromboembolism (VTE), which includes both DVT and pulmonary embolism (PE), increases 20-fold in male-to-female people using hormone treatment, especially estrogen. A meta-analysis published in 2019 in the Journal of Blood Medicine reviewed 13 studies that looked at the effects of hormone therapy, including which types of estrogen are used, on transgender men and women. It found that even though the risk of VTE increased with certain formulations of hormone therapy, the absolute clinical risk is low. The researchers recommended that ethinyl estradiol and progestins be avoided in transgender people. Your doctor should already understand the potential clotting risks that come with some hormone therapies, especially estrogen, but it’s still important to advocate for yourself and know the warning signs of DVT.
How Does DVT Affect Men and Women Differently?
Some research has shown that sex appears to impact the location in which deep vein clots form. A meta-analysis published in December 2018 in Thrombosis Research found that while women were more likely to have a distal DVT (located below the knee in the calf veins) than men, men had a higher proportion of proximal DVT (located in the popliteal, femoral, or iliac veins). The reasons for sex-specific differences in the location of DVTs are not fully understood, but risk factors like age and hormones may play a role. For example, being pregnant or taking birth control medicines are risk factors that may also contribute to the location of DVT in women, but more research is needed to understand how different risk factors may affect the location of DVT in men and women. Other studies have explored the role of gene mutations on the outcomes of patients with venous thromboembolism. While men and women are at equal risk for gene mutations that can cause clotting, biological sex may affect clinical outcomes. A study published in March 2017 in Thrombosis Research found no differences between men and women in the incidence of gene mutations that made them more susceptible to clotting when taking anticoagulant therapy to prevent recurrences of venous thromboembolism or major bleeding. But after anticoagulant therapy was discontinued, men with the gene mutation factor V Leiden (FVL), which is known to increase the chance of blood clotting, were at an increased risk for DVT compared with women with FVL.
Hormones and Hormone-Based Medications Play a Role
For women, Jorge Antonio Gutierrez, MD, a cardiologist and an assistant professor of medicine at Duke University in Durham, North Carolina, says, “It’s important to remember that hormonal changes that occur with contraception use, infertility treatments, or pregnancy increase the baseline risk of DVT during the reproductive years." The absolute risk for clotting in women is low, but that increases during pregnancy. Pregnant women are 5 times more likely to experience a blood clot compared with women who are not pregnant, according to the CDC, and PE is the leading cause of death in women during or just after having a baby. Having a clotting disorder may affect pregnancy. According to the U.S. National Library of Medicine, women who carry the FVL mutation are 2 to 3 times more likely to miscarry, and having a Cesarean section can raise your risk of pregnancy-related clotting. You can reduce your risk by limiting the time you spend sitting in one place — even if you get up just to stretch. When it comes to contraception, combined oral contraceptives that contain progestin pose less of a clotting risk than estrogen contraceptives, but they still slightly raise risk, according to a review published in June 2018 in the International Journal of Gynaecology and Obstetrics. If you’re a woman on birth control or hormone replacement therapy, or you are pregnant, your healthcare provider should evaluate your risk for DVT. A thorough health history and physical exam will be done in conjunction with patient education to reduce the risk of DVT. “It’s important to educate patients on the signs and symptoms of DVT,” says Dr. Gutierrez. “Patients should be taught to look out for increased leg swelling, skin that is warm to the touch near an area where clots normally form, or pain in a leg while taking birth control or during pregnancy.”
Lifestyle and Other Medical Factors Are Important for All Genders
For everyone, smoking and obesity are strong and preventable risk factors for DVT. Not using tobacco is one of the best things you can do to reduce your risk for DVT. Keeping active is also important, though sometimes that’s easier said than done. “For both sexes, major surgery, major trauma, or periods of immobility also put you at increased risk for DVT,” says Dr. Piazza. “That’s when decisions need to be made about whether DVT prophylaxis may be needed.” DVT prophylaxis is when you take steps to prevent blood clots in the deep veins, either by taking anticoagulant medications or wearing compression socks. A study published in July 2019 in the European Journal of Preventive Cardiology found that women who were active at their jobs and those who were active at least once a week had a lower risk of developing their first venous thromboembolism, though the correlation was inconsistent in men. This doesn’t mean exercise isn’t important for all genders, just that some may need other interventions. Age is another key risk factor for DVT. The risk of developing DVT is higher for people older than 65. “Although we can’t change our age, we can change certain factors like our level of mobility,” says Piazza. “For some patients who are at high enough risk for DVT, that may require proactive prevention like prophylactic anticoagulants or devices.” Additional reporting by Kaitlin Sullivan.
