Acute Myocardial Infarction and Oral Contraceptives

Abstract & Commentary

Synopsis: Low-dose oral contraceptives are not associated with an increased risk of myocardial infarction in women without cardiovascular risk factors.

Source: WHO Collaborative Study Lancet 1997; 349:1202-1209.

The world health organization collaborative study of cardiovascular disease and steroid hormone contraception reports a case-control study examining a possible association between myocardial infarction (MI) and low-dose oral contraception (OC). A total of 368 cases were matched with 941 controls. The cases were derived from women in Africa, Asia, Europe, and Latin America, from a total of 21 medical centers. There was a four- to five-fold overall increased risk of acute MI in current users of low-dose OC. In those women who reported no cardiovascular risk factors and had their blood pressure routinely checked before oral contraceptive use, there was no increased risk of MI. In those OC users who smoked, the risk of MI was increased 20-fold. For the first time, it is reported that women who had hypertension during pregnancy had an increased risk of MI with OC use. Comparing the risk of MI between users of OCs with less than 50 mcg of estrogen and those with 50 or more mcg of estrogen, there was no apparent effect of the dose of estrogen on the relative risk. The authors conclude that the degree of risk associated with OCs is substantial only among older women who smoked.


It is a familiar story that higher-dose OCs were associated with an increased risk of acute MI. This is the first substantial case-control study of the modern era reflecting the use of lower-dose OCs. There has been great interest that the new generation of progestational agents, being less androgenic, might be associated with protection against cardiovascular disease in OC users. It is important to note that the number of cases on third-generation progestational agents was insufficient to provide an accurate assessment whether MI risk was affected by the type of progestin.

I believe this report from WHO has several important points. First, the increased risk of MI was present in those women who used OCs and received poor or absent screening from clinicians. Thus, the cases of MI were essentially restricted to those patients who had chronic underlying disease and/or were smokers older than 35 years. This emphasizes the importance of providing good education and care in helping patients choose the most appropriate method of contraception. The most important risk factors identified in this study that can help us with better consultations are:

· a history of hypertension

· smoking

· being overweight

With appropriate screening of patients, the risk of MI with modern OCs is negligible.

A second point made by the WHO report is that, for the first time, there is a link between hypertension in pregnancy and the risk of MI in current users of OCs. It seems logical to me that this apparent link is also influenced by underlying chronic disease. It is likely that many of these patients had underlying chronic hypertension and, therefore, fall into the category of patients with risk factors.

The third point is that virtually all the cases were in older women. This, too, makes sense, as it is with increasing age that the associated risk factors begin to have an effect on clinical events. This makes it even more important that women older than 35 years have excellent screening for risk factors prior to receiving prescriptions for oral contraceptives. The WHO report also makes it clear that duration of use and past use do not affect the risk of MI.

Over the years, there has been recurring discussion whether to provide OCs over the counter. Evidence in this report makes a striking argument against such a move. The increased risk of MI was most evident in developing countries, where 70% of the cases received their OCs from a non-clinical source. Thus, deprived of screening in the developing countries, many patients with risk factors used OCs without adequate screening, and these patients were exposed to greater risk. The bottom line is that one would expect an appreciable increase in the rate of MI in OC users only among older women who smoke. This is not new information, but this study reemphasizes the importance of providing good clinical care and appropriate screening prior to the prescription of OCs.