Ischemic stroke risk low for OC users
Oral contraceptive (OC) users screened for hypertension have little, if any, increase in the risk of ischemic stroke, according to the latest research on the subject.1 A matched case-control study of women ages 16 to 44 in 16 centers in five European countries looked at risks in OC users, including those taking pills with third-generation progestins desogestrel and gestodene. (Recent studies have reviewed risks of venous thromboembolism with such pills, finding risk reports may have been premature. See Contraceptive Technology Update, December 1997, p. 145.)
"There is no difference between the risk of oral contraceptives of the third- and second-generation; only first-generation oral contraceptives seem to be associated with a higher risk," wrote researchers with Transnational Research Group on Oral Con-traceptives and the Health of Young Women in Berlin. "This small increase in risk may be further reduced by efforts to control cardiovascular risk factors, particularly high blood pressure."
The estimated relative risk of ischemic stroke in current OC users in that study (3 to 4) is similar to the estimate reported by the World Health Organi-zation (WHO) in Geneva, Switzerland,2 says Diana Petitti, MD, director of research and evaluation at Kaiser Permanente - Southern California in Pasadena. (For results of the WHO study and a study of OC users in the Kaiser-Permanente system, see CTU, December 1996, p. 148.)
"The estimates from these two studies are substantially higher than estimates of the relative risk of ischemic stroke derived from two recently published studies from the United States: the Kaiser-Permanente study and the Seattle study,"3,4 Petitti says. "In both U.S. studies, the estimated relative risk of ischemic stroke in current OC users was essentially 1.0."
Why the difference? "Differences between the U.S. studies and the WHO and Transnational studies are probably due to methodologic differences between the U.S. and the international studies and to real differences in risk that derive from differences in clinical practices regarding blood pressure screening and use of hypertension as a contraindication to OC use," she explains.
Both U.S. studies used control groups composed of community controls, she says. Hospital controls were used in the WHO study, while the transnational control group used for the main analysis was a mix of hospital and community controls. In the transnational study, the estimated relative risk of ischemic stroke using only hospital controls was much higher (about 7) than the risk based on community controls - about 2.5.
In both studies, a high proportion of OC users didn't have their blood pressure checked before using pills; the relative risk of ischemic stroke was higher in this group in both studies. For women in the international study who had their blood pressure checked, the estimated relative risk was essentially the same as in the U.S. studies, Petitti says. Neither U.S. study could examine the relative risk of ischemic stroke separately in women who had diagnosed high blood pressure, since only a handful of such women were current OC users.
Researchers with the transnational study estimate three strokes per 100,000 women per year may be attributed to OC use, with this risk controlled by avoiding prescription to women with cardiovascular risk factors such as high blood pressure and managing such risk factors.
In some cases, benefits outweigh the slight risks, says Lothar A. J. Heinemann, MD, DSc, director and professor of ZEG-Centre for Epidemiology and Health Research in Berlin and lead author of the transnational study. "In young women, say under 35, who are healthy, do not smoke, and do not have elevated blood pressure, the risk to suffer from cardiovascular events is so small that you can almost ignore it for public health decisions, particularly if you compare with the benefits. Even so, the long-term effects of OCs will be further monitored from the scientific community, rather more on a routine basis than because of particular concern."
References
1. Heinemann LA, Lewis MA, Thorogood M, et al. Case-control study of oral contraceptives and risk of thromboembolic stroke: Results from International Study on Oral Contraceptives and Health of Young Women. BMJ 1997; 315:1,502-1,504.
2. WHO Collaborative Study of Cardiovascular Disease and Steroid Hormone. Ischaemic stroke and combined oral contraceptives: Results of an international, multicentre, case-control study. Lancet 1996; 348:498-505.
3. Petitti DB, Sidney S, Bernstein A, et al. Stroke in users of low-dose oral contraceptives. N Engl J Med 1996; 335:8-14.
4. Schwartz SM, Siscovick DS, Longstreth WT Jr., et al. Use of low-dose oral contraceptives and stroke in young women. Ann Intern Med 1997; 127(8 Pt 1):596-603.
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