Image by Andre E.X. Brown
Results of a case-control study indicate that estrogen-only hormone therapy carries a lower risk of venous thromboembolism (VTE) than combined estrogen-progestogen therapy.
The study also suggests the type of progestogen a patient receives does not significantly impact the risk of VTE, but the route of administration for estrogen does.
Annica Bergendal, MD, PhD, of Karolinska Institutet in Stockholm, Sweden, and her colleagues reported these findings in Menopause.
The study was conducted in Sweden between 2003 and 2009. It included 838 women with VTE and 891 age-matched control subjects.
Analyses suggested the risk of VTE was almost 2-fold higher in women currently on hormone therapy than in those not taking hormones. The odds ratio (OR)—which was adjusted for smoking, body mass index, and immobilization—was 1.72 (95% CI 1.34-2.20).
Women who took combined estrogen-progestogen therapy had nearly 3 times the VTE risk of those who took no hormones (OR 2.85, 95% CI 2.08-3.90), but the risk was much lower for women who took estrogen alone (OR 1.31, 95% CI 0.78-2.21).
The risk of VTE with combined estrogen-progestogen treatment was about double that of estrogen alone (OR 2.18, 95% CI 1.21-3.92).
Researchers have wondered whether the type of progestogen used makes a difference in the risk of VTE, but this study didn’t show any significant difference in risk between 2 commonly used progestogens.
When oral estrogen was combined with progestogen, the risk of VTE was somewhat, but not significantly, higher among users of medroxyprogesterone acetate (OR 2.94, 95% CI 1.67-5.36) than among users of norethisterone acetate (OR 2.29, 95% CI 1.50-3.40).
On the other hand, the way estrogen was delivered appeared to impact the risk of VTE, with oral estrogen conferring the highest risk.
When the researchers used transdermal estrogen—given alone—as reference, they observed an increased risk of VTE associated with oral estrogen alone (OR 1.84, 95% CI 0.62-5.52).
And when the researchers used locally (vaginally) administered estrogen alone as reference, they saw an increased risk of VTE associated with oral estrogen alone (OR 2.64, 95% CI 1.30-5.38).
Among women using combined estrogen-progestogen treatment, with transdermal estrogen as a reference, there was an increase in VTE risk associated with oral estrogen (OR 2.21, 95% CI 0.88-5.60).
“This study adds to our knowledge that transdermal estrogen therapies are safer than oral, and that different estrogen or progestogen combinations may have different risks,” said JoAnn V. Pinkerton, MD, executive director of the North American Menopause Society, who was not involved in this study.
“The lack of blood clots with transdermal estrogen and with vaginal estrogen is very reassuring for women who need to continue taking hormones as they age, when risk of blood clots increases.”
