However, a study carried out on 217 women with a first myocardial infarction before the age of 50 years, and 763 healthy control women showed that the risk is substantially elevated among women with various inherited clotting factor defects ⁽¹⁰⁾. 

The overall odds ratio for myocardial infarction,  in the presence of a coagulation defect is 1.1. 

The combination of a prothrombotic mutation and current smoking, increases the risk of   myocardial   infarction   12-fold   compared   with   non-smokers,  without   a coagulation defect.

Among   women   who   smoke   cigarettes,  factor   V   Leiden presence versus absence increases the risk by 2.0, and prothrombin 20210A mutation presence versus absence has an odds ratio of 1.0 ⁽¹¹⁾.

Nevertheless, some studies reported that the risk of myocardial infarction does not appear to depend on coagulation abnormalities or the type of oral contraceptive. However, the risk is highest in the first year of use and increases in women with a previous venous thrombosis and with age.

In the past years was demonstrated, on 219 death from myocardial infarction, that the frequency of use of combined oral contraceptives (COCs), during the month before death was significantly greater in the group with infarction than in the control group and the average duration of use was longer ⁽¹²⁾. 

The lowering of the estrogen dose in COCs from 50 mcg to 20-30 mcg,  in the last decade,  clearly does not reduce the risk of myocardial infarction; although current opinions are conflicting ^(13,14). The effects in COC users with other risk factors for venous thrombosis tend to be less pronounced and more inconsistent. 

A number of studies have found higher relative risks among current users of low estrogen dose COCs containing desogestrel or gestodene, than among users of similar products containing levonorgestrel ⁽¹⁴⁾.

A number of explanations,  in terms of bias or confounding,  have been proposed for these clinically small differences. At best,  empirical evidence for these explanations is weak. 

A transnational study carried out on 182 women aged 18-44 with myocardial infarction (MI)  compared with 635 women without MI reported overall odds ratio for MI for second generation COC versus no current users of 2.35 and 0.82 for third generation. A direct comparison of third generation users with second generation users yielded an OR of 0.28(OR=odds ratio).