The risk of venous thromboembolism (VTE) associated with the use of chlormadinone acetate (CMA) compared to the gold-standard progestin levonorgestrel (LNG) as component of combined oral contraceptives (COC) is currently unknown. The Pharmacovigilance Risk Assessment Committee (PRAC) of the European Medicines Agency (EMA) recommended a pooled analysis of four prospective cohort studies carried out by the Berlin Center for Epidemiology and Health Research (ZEG Berlin) in order to clarify whether CMA-containing COCs carry a different VTE risk compared to LNG-containing COCs.

This study is designed as a retrospective cohort study. ZEG Berlin conducted several large prospective cohort studies on the risk of VTE associated with the use of hormonal contraceptives. Four of these studies included a substantial number of women using CMA/EE or LNG/EE-containing COCs. For this study, the data on CMA/EE and LNG/EE from the following four prospective cohort studies are combined: 1) EURAS-OC/LASS 2) INAS-OC 3) INAS-SCORE and 4) INAS-FOCUS.

Participants will be identified retrospectively from a pooled dataset which comprises four large, controlled, prospective, non-interventional active surveillance studies that focused on the risk of VTE associated with the use of combined oral contraceptives. All data were prospectively collected by ZEG Berlin and follow the EURAS/INAS study design. Inclusion and exclusion criteria, the method of patient recruitment and follow-up as well as research methods were similar across studies.

The EURAS-OC/LASS study was conducted in Europe only; the other three studies are transatlantic studies that include subjects from both Europe and the United States of America.

This analysis is specifically designed to assess the risk of VTE associated with the use of COCs containing CMA/EE compared to LNG/EE.

Inclusion: female, aged 15 to 49 years, participation in one of the 4 observational studies conducted between 2000 and 2019 (LASS/EURAS-OC, INAS-OC, INAS-SCORE, INAS-FOCUS), COC new user (starters, switchers, and re-starters), applied COCs: CMA/EE or LNG/EE.

Exclusion of women with a personal history of VTE.

Participants will be identified retrospectively from a pooled dataset which comprises four large, controlled, prospective, non-interventional active surveillance studies that focused on the risk of VTE associated with the use of combined oral contraceptives. All data were prospectively collected by ZEG Berlin and follow the EURAS/INAS study design. Inclusion and exclusion criteria, the method of patient recruitment and follow-up as well as research methods were similar across studies.