From the American College of Obstetricians and Gynecologists re stroke and transdermal HRT:
https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/04/postmenopausal-estrogen-therapy-route-of-administration-and-risk-of-venous-thromboembolism
“Studies that compared oral and transdermal ET have demonstrated that transdermally administered estrogen has little or no effect in elevating prothrombotic substances and may have beneficial effects on proinflammatory markers, including C-reactive protein, prothrombin activation peptide, and antithrombin activity. Also, in contrast to oral ET, transdermal ET also may have a suppressive effect on tissue plasminogen activator antigen and plasminogen activator inhibitor activity 2324 25 26 27 28 29.

The Estrogen and Thromboembolism Risk study, a multicenter case–control study of thromboembolism among postmenopausal women aged 45–70 years, demonstrated an odds ratio for venous thromboembolism in users of oral and transdermal estrogen to be 4.2 (95% CI, 1.5–11.6) and 0.9 (95% CI,0.4–2.1), respectively, when compared with nonusers 10. Transdermal estrogen had no increased risk compared with nonusers. Similar results were reported elsewhere 30 31 32 33 34 35 and of particular importance, in women who were stratified for weight 36 and the presence of prothrombotic mutations 37.”