Transgender women on hormone therapy twice as likely to suffer from blood clots

But the risk from estrogen therapy is still small, researchers say.

New research finds that transgender women are at an increased risk of vascular problems, especially blood clots. Researchers attribute this risk to estrogen hormone therapy, which is often part of a male-to-female transition.

Many transgender people take hormones, like estrogen or testosterone, to bring their bodies into alignment with their gender identity. In a 2015 survey in the United States, 95 percent of transgender respondents said they wanted hormone therapy to be part of their gender transition. 71 percent said they had already received at least some hormone therapy.

While much research has been conducted on hormone therapy in postmenopausal women, not enough is known about how the practice could affect the long-term health of transgender people. The new study is part of a growing body of research seeking to address this gap.

“The body of transgender health research is growing, but high quality data are still lacking with respect to many critical gaps in knowledge,” Michael Goodman, an epidemiologist at Emory University and one of the study’s authors.

Blood clots are twice as likely for transgender women

The researchers analyzed health data from 4,960 transgender and gender non-conforming people, as well as 97,461 cisgender patients (cisgender refers to people who are not transgender). They found that transgender women were nearly twice as likely to experience a venous thromboembolism, a type of blood clot that can lodge in the lungs, as cisgender men and women. “Based on our data, the differences between transwomen and cisgender people are likely attributable to estrogen therapy,” said Goodman.

When researchers narrowed their scope to trans women who’d started their estrogen therapy at the health system that provided the data—giving a more complete picture of their treatment—they also found greater risk of stroke. The risks for both stroke and blood clots were particularly high two to six years after the women started taking estrogen.

Testosterone therapy was not found to increase risk in transgender men, but data for this group was not as conclusive.

Risks still within an acceptable margin

The researchers say their results don’t necessarily mean that estrogen therapy is a bad idea, and risks need to be weighed against the benefits of treatment. Another of the study’s authors, Joshua Safer of the Mount Sinai Center for Transgender Medicine and Surgery, points out: “Most hormones used for trans people are old and relatively safe. When estrogen therapy is used correctly, the blood clot risk is true, but small enough that most patients are likely to find it acceptable.” He also notes that estrogens presenting even greater clotting concerns are still used in birth control pills.

More research could help pinpoint whether certain estrogen formulations, doses, and ways of delivering the hormone are lower risk than others, or perhaps present no increased risk at all. Safer said: “This study represents an improvement in research on trans people, but the landscape remains quite barren with numerous large gaps. There’s much to be investigated in greater detail.”

Featured image courtesy of Donald Bliss.