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Good news to share with your patients: According to the latest published research, there is no significantly increased risk of acute myocardial infarction (AMI/heart attack) in women who use oral contraceptives (OCs).1 Even more important, scientists were unable to find evidence of a difference between second- and third-generation OCs when it comes to heart attack risk.
These results come from a retrospective community-based, case-controlled study, conducted in England, Scotland, and Wales, in which researchers examined the association between OC use and heart attack in women under age 45.
A total of 448 women ages 16 to 44 who had suffered a heart attack were matched with 1,728 women in the control group. Main outcome measures were odds ratios for heart attack in current users of all combined OCs stratified by their progestin content compared with non-users, as well as a comparison of current users of third-generation vs. second-generation pills.
"There is no association between any type of modern low-estrogen dose OC and myocardial infarction," says Nicholas Dunn, MA, DM, MSc, MRCGP, senior research fellow at the Drug Safety Research Unit at Bursledon Hall in Southampton, UK, and lead author of the study. "Women who have any of the classical risk factors for AMI, most notably smoking, should be warned that it is these risk factors that are of importance — not the OC that they may be taking."
Researchers for the current investigation were involved as a collaborating center in the "transnational study," a multinational case-control study on thrombotic effects of OCs. This study was ended prematurely in 1995, due to what has been dubbed "the pill scare" in the United Kingdom. (See Contraceptive Technology Update, October 1996, p. 126, for more information on research affected by concerns surrounding third-generation pills containing gestodene and desogestrel.)
"This left unfinished business on the AMI question, and for this reason, we designed the study to have sufficient power to answer the question as to whether there was a difference between second- and third-generation OCs," notes Dunn.
The present study could not confirm a differential effect on the risk of AMI between oral contraceptives with second- and third-generation progestins, says Øjvind Lidegaard, MD, assistant professor of obstetrics and gynecology at Herlev Hospital, University of Copenhagen in Denmark. He wrote a commentary on the study, and both were published in the British Medical Journal.2 This study offers different results from a 1997 case-controlled investigation conducted in 16 centers in Germany, the United Kingdom, France, Austria, and Switzerland.3 In that study, a significantly lower risk of heart attack was found when comparing use of third-generation OCs with use of second-generation OCs.
Researchers involved in the UK study found that of those women under age 45 who suffered a heart attack, 87% were not taking any oral contraceptive. The majority of women who had a heart attack had at least one or more known cardiovascular risk factors.
While the risk for heart attack among women under 45 is rare, young women who wish to preserve their cardiovascular risk should be advised to stop smoking above all other actions, note the researchers. Smoking was strongly associated with heart attack, results showed. "Three out of four AMIs in young women would be prevented if all women stopped smoking," Lidegaard advises.
Dunn sees the results from the current study as "fairly conclusive" on the OC/AMI question. "However, our data has thrown up interesting questions regarding regional variation in incidence and case fatality of AMI among this age group of women in the UK," he notes. "We shall be looking into this further."
Many older studies have demonstrated a significantly increased risk of thrombotic diseases, including AMI, in current users of oral contraceptives, notes Lidegaard. This increased risk seems to apply primarily to older high-dose oral contraceptives. "Generally, studies demonstrating risks in users of oral contraceptives are the object of more attention than reassuring studies like this one," says Lidegaard of the UK study. "In order to ensure a balanced impression of oral contraceptives, it is important also to focus on the good news, so that some of the concern, which many people might have had, can be eliminated."
1. Dunn N, Thorogood M, Faragher B, et al. Oral contraceptives and myocardial infarction: Results of the MICA case-control study. BMJ 1999; 318:1,579-1,584.
2. Lidegaard Ø. Commentary: Oral contraceptives and myocardial infarction: Reassuring new findings. BMJ 1999; 318:1,583-1,584.
3. Lewis MA, Heinemann LA, Spitzer WO, et al. The use of oral contraceptives and the occurrence of acute myocardial infarction in young women. Results from the Transna tional Study on Oral Contraceptives and the Health of Young Women. Contraception 1997; 56:129-140.