ACUTE MYOCARDIAL-INFARCTION AND COMBINED ORAL-CONTRACEPTIVES - RESULTS OF AN INTERNATIONAL MULTICENTER CASE-CONTROL STUDY

Background The association between oral contraceptive (OC) use and acu te myocardial infarction (AMI) was established in studies from norther n Europe and the USA, which took place during the 1960s and 1970s. Few data are available to quantify the risk worldwide of AMI associated w ith use of OCs introduced since those early studies. This hospital-bas ed case-control study examined the association between a first AMI and current OC use in women from Africa, Asia, Europe, and Latin America (21 centres). Methods Cases were women aged 20-44 years who had defini te or possible AMI (classified by history, electrocardiographic, and c ardiac-enzyme criteria), who were admitted to hospital, and who surviv ed for at least 24 h. Up to three hospital controls matched by 5-year age-band were recruited for each of the 368 cases (941 controls). All participants were interviewed while in hospital with the same question naire, which included information on medical and personal history, lif etime contraceptive use, and blood-pressure screening before the most recent episode of OC use. Odds ratios compared the risk of AMI in curr ent OC users and in non-users (past users and never-users combined). F indings The overall odds ratio for AMI was 5.01 (95% CI 2.54-9.90) in Europe and 4.78 (2.52-9.07) in the non-European (developing) countries ; however, these risk estimates reflect the frequent coexistence of ot her risk factors among OC users who have AMI. Very few AMIs were ident ified among women who had no cardiovascular risk factors and who repor ted that their blood pressure had been checked before OC use; odds rat ios associated with OC use in such women were not increased in either Europe or the developing countries. Among OC users who smoked ten or m ore cigarettes per day, the odds ratios in Europe and in the developin g countries were over 20. Similarly, among OC users with a history of hypertension (during pregnancy or at any other time), odds ratios were at least ten in both groups of countries, No consistent association b etween odds ratios for AMI and age of OC users or oestrogen dose was a pparent in either group of countries, No significant increase in odds ratios was apparent with increasing duration of OC use among current u sers, and odds ratios were not significantly increased in women who ha d stopped using OCs, even after long exposure. The study had insuffici ent power to examine whether progestagen dose or type had any effect o n AMI risk. Interpretation Current use of combined OCs is associated w ith an increased risk of AMI among women with known cardiovascular ris k factors and among those who have not been effectively screened, part icularly for blood pressure, AMI is extremely rare in younger (<35 yea rs) non-smoking women who use OCs, and the estimated excess risk of AM I in such women in the European centres is about 3 per 10(6) woman-yea rs. The risk is likely to be even lower if blood pressure is screened before, and presumably during, OC use. Only among older women who smok e is the degree of excess risk associated with OCs substantial (about 400 per 10(6) woman-years).