Mortality from venous thromboembolism and myocardial infarction in young women in the Netherlands

Mortality from venous thromboembolism in young Swedish women and its relation to pregnancy and use of oral contraceptives – an approach to specifying rates

BACKGROUND

Pregnancy and use of combined oral contraceptives (COCs) are major risk factors for venous thromboembolism (VTE) in young women and we wanted to obtain accurate VTE mortality data overall, by age, associated with the use of COCs and pregnancy.

METHODS

From the Swedish Cause of Death Register (CDR) we identified women aged 15-44 with VTE as underlying or contributory cause of death during the period 1990-1999. We scrutinized medical records and included verified VTE cases without active cancer or terminal disease. Pregnancy statistics and COC utilization data were obtained from national databases.

RESULTS

Of the 120 cases included, 9 (8%) were associated with pregnancy and 28 (23%) with current COC use. The overall refined VTE mortality rate in current COC users was 7.5[4.7; 10.3] per million user-years and the corresponding pregnancy-related rate was 8.9[4.1;17.0] per million pregnancy years, rates increasing with age. For ages 15-24, the rate was significantly higher in current COC users than in non-pregnant women not using COCs: 6.0[3.1; 10.5] per million user-years vs. 0.3[0.0; 1.2] per million woman years. Underlying cause mortality data included 82% of VTE deaths associated with COCs, and 56% of maternal deaths had a pregnancy-related code.

CONCLUSION

Mortality figures from VTE associated with the use of COCs and pregnancy were similar. COC use had an important impact on the total VTE mortality in the youngest age group. Standard mortality statistics do not allow accurate monitoring of VTE mortality in young women due to missing data, misdiagnoses and coding rules.

Thrombophilias and gynaecology

In gynaecology, women are exposed to sex steroids when using oral contraceptives, hormone replacement therapy or when undergoing in vitro fertilization treatment and ovulation induction. Oral contraceptives and the use of hormone replacement therapy increase the risk of venous thrombosis. The risk is highest in the first year of use and higher among women with clotting defects. Women taking third-generation oral contraceptives have an almost twofold increased risk of venous thrombosis compared with those taking second-generation oral contraceptives. Inherited clotting defects, which are themselves risk factors of venous thrombosis, (e.g. factor V Leiden mutation, deficiency of protein C, protein S or antithrombin, high plasma levels of factor VIII, and prothrombin mutation) appear synergistically increase the risk of venous thrombosis caused by oral contraceptives. Recent studies also point to an interaction between hormone replacement therapy and coagulation defects in causing venous thrombosis. Emerging studies show that in vitro fertilization treatment and ovulation induction are also risk factors for venous thrombosis; the role of coagulation defects in this association is not yet clear.

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.

Oral contraceptives and thrombosis

Oral contraceptives (OCs) are used by many millions of healthy young women. Their ease of use and efficacy against unwanted pregnancy has made them an indispensable part of modern society. Despite various changes in formulation, they are clearly associated with an increased risk of venous thromboembolism (VTE). Case-control and prospective studies have developed a range of relative risks of VTE, but the important issue is the impact of VTE relative to perceived benefits of the OC. This involves societal as well as medical judgment. The development of third-generation OCs has led to considerable concerns that these newer preparations may be associated with additional thrombotic risks over and above those of the traditional second-generation preparations. The paradoxical effect, that a change in progestogen in the combined OC could lead to increased VTE, could be explained by the induction of activated protein C resistance. In a society that is less prepared to accept unwanted side effects from medications, it is recommended that increased attention be given to patient selection, and possibly the incorporation into this process of some of the more recently discovered hypercoagulability markers.

Third- and second-generation oral contraceptives are associated with similar risk estimates for venous thromboembolism

A scientific discussion between 1995 and 1999 addressed the question whether second- and third-generation oral contraceptives (OCs) were associated with different risks of venous thromboembolism (VTE). Results from three epidemiological studies became available in the course of 1995, in which such differences were observed. Although it was unclear at that time whether these observations reflected causality or were induced by bias and/or confounding, some regulatory bodies in Europe restricted the indication for use of third-generation oral contraceptives. Immediate media attention generated a pill scare in those, but also other, countries. Indications for the influence of bias were observed in the initial studies of 1995 and further substantiated in subsequent utilization and prescribing surveys. The most important bias seemed to be related to differences in age and duration of use between third- and second-generation OC users. A number of new studies as well as new analyses in two of the 1995 databases included measures to limit the effect of the identified biases/confounders. These studies observed similar risks of venous thromboembolism with second- and third-generation oral contraceptives. Two other recently published studies did not or could not include the same level of control for confounding and reported similar results as the 1995 studies, thus reconfirming the relevance of the identified confounders. Population data show that the massive switch in the UK from third-generation OCs to second-generation OCs in 1995 has not resulted in a reduction of the incidence of VTE in OC users after 1995, illustrating that the risk of VTE is not determined by the type of low-dose pill used. In addition, data from trend analyses, spontaneous reporting and studies addressing hemostatic mechanisms in pill-users also do not support a potential difference in risk of VTE between users of second- and third-generation OCs.

Newer oral contraceptives and the risk of venous thromboembolism

Research on the relationship between venous thromboembolism and the progestagen content of combined oral contraceptives has pointed to an increase in risk associated with products containing desogestrel and gestodene. Although many biases must have been at play in these nonexperimental studies, the errors that have been suggested and examined are not of a sufficient magnitude to account for the observed results. The most plausible explanation of the available data is that combined oral contraceptives containing desogestrel and gestodene carry a very small risk of venous thromboembolism, which exceeds the even smaller risk carried by products containing levonorgestrel. The position of norgestimate is uncertain.

Mortality from venous thromboembolism among young women in Europe: no evidence for any effect of third generation oral contraceptives

STUDY OBJECTIVE

To investigate whether there has been an increase of venous thromboembolism (VTE) mortality in European countries, concurrent with the replacement of second generation by third generation combined oral contraceptives (COCs). Such an increase has been predicted, and reportedly detected, because published studies have detected an increased incidence of VTE associated with third generation rather than second generation COC use.

DESIGN

Data were collected on population and annual VTE mortality in women 15-34 and 35-49 years old, and on second and third generation COC sales, from 1981 to 1994 in 13 European countries. Data from the seven most populous countries were analysed by linear regression of annual VTE mortality, in the 15-34 and 15-49 age groups, with respect to calculated total and third generation COC use rates, and the regression coefficients used to estimate mortality differences between second generation users and non-users and between third and second generation users, respectively.

MAIN RESULTS

The estimated mortality differences in all seven countries had confidence intervals wide enough to contain both zero and the excess mortalities expected from the results of published studies. This was true both for the mortality difference between third and second generation COC users and for that between second generation users and COC non-users.

CONCLUSIONS

Mortality differences of the size expected from the published studies cannot be measured using annual national VTE mortality and COC sales data alone, because of residual interannual variation in VTE mortality, and possibly confounding between rising third generation market share and total COC use.

Third-generation oral contraceptive and deep venous thrombosis: from epidemiologic controversy to new insight in coagulation

Four epidemiologic studies showed a twofold increase in risk of deep venous thrombosis with the use of oral contraceptives containing third-generation progestins, relative to second-generation products. These findings have been strongly debated ever since, and new studies have been added. In the current article we examine whether the findings can be explained by potential biases or other shortcomings of the epidemiologic studies. We conclude that complete certainty cannot exist but that the most rational conclusion from the epidemiologic findings and their discussion is that an increased risk of deep venous thrombosis with third-generation contraceptives is likely, especially in first-time and young users. The controversy has recently led to new insights in coagulation: Women who use third-generation contraceptives acquire a resistance to the blood's own anticoagulation system, similar to the activated protein C resistance that is seen in persons who carry the factor V Leiden mutation but different from that in women using second-generation contraceptives.