A multinational case-control study of cardiovascular disease and steroid hormone contraceptives. Description and validation of methods. World Health Organization Collaborative Study of Cardiovascular and Steroid Hormone Contraception

A hospital-based, case-control study of the association between current usage of oral contraceptives and first-time cases of acute myocardial infarction, stroke, or a venous thromboembolic event (deep vein thrombosis or pulmonary embolus) was carried out in 17 countries from four regions (Africa, Asia, Europe, and Latin America). A total of 3792 cases and 10,281 hospitalised controls matched for age were recruited during a 4-year period, ending in June 1993. The study was designed to have sufficient power to detect a relative risk of 2 for developing each of the three study diseases, associated with current oral contraceptive use in each of the four regions, with the exception of acute myocardial infarction (for which all non-European regions were to be combined) and for venous thromboembolic events in Asia, where these disorders are rare. This report describes the background, pilot study, methods, and the analyses carried out to validate the methods used in the study.

Oxidative status and oral contraceptive. Its relevance to platelet abnormalities and cardiovascular risk

Oral contraceptive (OC) use is a risk for thrombogenic events. This paper reviews effects of OC on oxidative status, coagulation, and platelet activity. Complicating effects of cardiovascular risk factors such as smoking, diabetes, hyperpidemia, and hypertension, are discussed. From these data we conclude that: 1. OC use modifies slightly but significantly the oxidative status in women and in animals by decreasing in plasma and blood cells the antioxidant defenses (vitamins and enzymes). 2. The changes in the oxidative status are related to an increase in plasma lipid peroxides apparently responsible for the hyperaggregability and possibly the imbalance in clotting factors associated with the OC-induced prethrombotic state. 3. These effects of OC appear to be increased by a high intake of polyunsaturated fat and counteracted by supplements of vitamin E. 4. The risk factors acting synergistically with OC, have all been shown to increase platelet reactivity. In addition, smoking, diabetes, and, to some extent, dyslipidemia are associated with an increased level of lipid peroxides and concomitant changes in the antioxidant defenses that can be additive to those induced by OC. Thus, free radicals and lipid peroxidation could be the underlying mechanism in the predisposition to thrombosis induced by most risk factors in OC users. 5. Results of epidemiologic and experimental studies in this field will be concordant only when diet and natural antioxidants will be systematically taken into consideration.

Oral contraception and post-operative thromboembolism: an epidemiological review

It has been stated that oestrogen-containing oral contraceptive medication should be discontinued one month prior to surgery, to avoid an increased incidence of post-operative thromboembolism. Others have suggested that the risk of post-operative morbidity is low compared with the risk of pre-operative pregnancy, and that in most cases no such action should be taken. The evidence from clinical investigation is reviewed, with particular reference to study design. It is found that all studies so far conducted are subject to sources of bias or confounding which render their results inconclusive. There is a need for a randomised control trial comparing the effects of discontinuing or continuing oral contraception prior to surgery. Meanwhile, with a post-operative risk inferred but not conclusively demonstrated, if oral contraception is to be withdrawn prior to surgery, great care must be taken to reduce the risk of ensuing pregnancy to as near zero as possible.

Oral contraceptive agents and breast cancer: a population-based case-control study

In this population-based case-control study that was conducted in Adelaide, South Australia, and which involved 395 case subjects and 386 control subjects who were aged 20 years to 69 years, the adjusted relative risk of breast cancer for women who had ever used oral contraceptive agents was 1.06 (95% confidence interval [CI], 0.70-1.60). Relative risks that were associated with use of oral contraceptive agents for one month to 18 months and for 19 months or more before a first pregnancy were 1.09 (95% CI, 0.45-2.62) and 1.67 (95% CI, 0.63-4.42), respectively, but the trend was not statistically significant. Relatively-little variation in risk was found in association with the total duration of the use of oral contraceptive agents and with years since the first and the last use of oral contraceptive agents. When the risk of breast cancer in association with the use of oral contraceptive agents was examined across levels of risk factors of breast cancer (history of benign breast disease, family history of breast cancer and parity), the only relative risk which deviated markedly from unity was that which was associated with use of oral contraceptive agents in women with a history of benign breast disease; however, the relative risk of 1.77 (95% CI, 0.35-8.97) was not statistically significant. In conclusion, the results of this study support those of the majority of previous studies in showing no overall relationship between the use of oral contraceptive agents and the risk of breast cancer.

Oral contraceptives and cardiovascular disease: a critique of the epidemiologic studies

Observational study designs used to investigate the relationship of oral contraceptive use to the occurrence of venous thromboembolism, stroke, myocardial infarction, and cardiovascular death include case-control, cohort, and mortality statistics studies. This analysis catalogs the findings of each of these epidemiologic studies, its statistical significance, and its performance with regard to scientific methodologic standards. An association between current oral contraceptive use and incidence of venous thromboembolism without predisposition has been consistently observed in case-control and cohort studies. Associations are less consistent for various types of stroke and for myocardial infarction. Only the Royal College of General Practitioners study found a significantly elevated risk of cardiovascular death with oral contraceptive use. The majority of mortality statistics studies offer little support for a relationship between oral contraceptive use and cardiovascular events. Major systematic problems in the epidemiologic studies include potential for bias in the detection of cardiovascular events and differences in the prognostic susceptibility of compared groups. Bias in the ascertainment of drug exposure is an unresolved issue for most of the case-control studies. Because of possible biases arising from methodologic deficiencies in these epidemiologic studies, questions as to the validity of the observed associations between oral contraceptive use and cardiovascular events should remain.