Pulmonary embolism in menopausal hormone therapy: a population-based register study.

OBJECTIVE: Oral but not transdermal menopausal hormone therapy (MHT) increases the risk of venous thromboembolism. There is no evidence regarding the risk of the serious complication pulmonary embolism (PE). The aim was to investigate the risk of PE in women using MHT depending on administration route, type of progestin and treatment duration. METHOD: The population-based case-control study covered 1,771,253 women aged 40-69 years, during 2006-2015. Diagnoses of PE (n = 13,974) and drug dispensations were received from national validated registers. RESULTS: Current MHT users had a higher risk of PE than non-users (odds ratio [OR] 1.15, 95% confidence interval [CI] 1.05-1.26). First ever users had the highest risk (OR 2.07, 95% CI 1.23-3.50). Transdermal administration was not associated with increased risk of PE. The OR was slightly but non-significantly higher with estrogen combined with medroxyprogesterone acetate than with norethisterone acetate. DISCUSSION: The risk of PE was significantly increased in users of oral but not transdermal MHT, with the highest risk in first ever users of oral estrogen combined with medroxyprogesterone acetate. The risk was considerably lower in women with recurrent treatment, probably because of the healthy user effect. CONCLUSION: PE was most common close to initiation of oral treatment. Transdermal MHT did not increase the risk of PE.