The impact of micronized progesterone on cardiovascular events - a systematic review.

Biologically identical menopausal hormone therapy (MHT) including micronized progesterone (MP) has gained much attention. We aimed to assess the impact of MP in combined MHT on venous and arterial thromboembolism (VTE/ATE) (e.g. deep venous thrombosis/pulmonary embolism, myocardial infarction [MI] and ischemic stroke). Articles were eligible if they provided endpoints regarding cardiovascular events and use of exogenous MP. Literature searches were designed and executed for the databases Medline, Embase, CINAHL, the Cochrane Library, ClinicalTrials.gov and interdisciplinary database Web of Science. Twelve studies consisting of randomized controlled trials (RCTs), case-control studies and prospective or retrospective cohort studies were included, and risk of bias was assessed. Only a minority assessed thromboembolic events as a primary endpoint, showing that in contrast to norpregnane derivatives, primary and recurrent VTE risk was not altered by combining estrogens with MP, which was also true for ischemic stroke risk. Similarly, in placebo-controlled RCTs assessing VTE/ATE as adverse events there were no significant intergroup differences. Studies on MI as a primary endpoint are missing. In conclusion, while available data suggest that MP as a component in combined MHT may have a neutral effect on the vascular system, more RCTs investigating the impact of MP alone or in combined MHT on vascular primary endpoints are needed.