The Risk of Venous Thromboembolism with Different Generation of Oral Contraceptives; a Systematic Review and Meta-Analysis

INTRODUCTION: Oral contraceptives (OCs) are considered as one of the most common risk factor of venous thromboembolism (VTE) in childbearing age. Some of the recent researches indicate that the odds of VTE may be even higher with newer generations of OCs. The present meta-analysis was designed to evaluate the effect of different generation of OCs on the occurrence of VTE. METHODS: Two researchers independently ran a thorough search in Pubmed, ISI Web of Science, EMBASE, CINAHL and Scopus databases regarding study keywords including thromboembolic event, thromboembolism, embolism, thromboembolic, thrombotic and thrombosis, combined with oral contraceptive. The outcomes were the incidence of diagnosed thromboembolism, such as deep vein thrombosis, pulmonary embolism and cerebral venous thrombosis. Based on the heterogeneity of the studies, random effect model was used and pooled odds ratio was reported. RESULTS: Three cohort and 17 case-control studies with 13,265,228 subjects were entered into meta-analysis. Analysis showed that the odds of VTE in women taking OCs are more than three-fold (OR=3.13; 95% CI: 2.61-3.65). The risk of VTE in women taking first-, second- and third-generation OCs are 3.5 fold (OR=3.48; 95% CI: 2.01-4.94), 3 fold (OR=3.08; 95% CI: 2.43-3.74) and 4.3 fold (OR=4.35; CI: 3.69‒5.01), respectively. CONCLUSION: It seems that the risk of VTE is not same between different generations of OCs, so that third-generation has highest risk. Taking second and third-generation OCs increases the risk of VTE up to 3 and 4.3 fold, respectively. The researchers of the present study suggest that more trials be designed in relation to the effect of newer generations of OCs in different communities.