Pill update: Despite risks, OCs add benefits
More news from the research front: Today’s low-dose combined oral contraceptives (OCs) are just as effective as the older, high-dose preparations in protecting women from ovarian cancer. Such health benefits, combined with its protection against pregnancy, outweigh a small increased risk of stroke posed by the Pill.
A just-published population-based, case-control investigation shows that women who are taking or have taken OCs with less than 50 mcg of estrogen have a 40% reduction in risk of ovarian cancer, the same risk reduction provided by the older, high-dose birth control pills.1 While there is a large body of literature documenting the effectiveness of older OC formulations, the new study represents the first of its design to offer a comprehensive look at the newer OCs, says lead author Roberta Ness, MD, MPH, associate professor of epidemiology, medicine, and obstetrics/gynecology at the University of Pittsburgh.
Study weighs the risks
A new meta-analysis conducted by University of California at San Francisco (UCSF) researchers indicates that risk of ischemic stroke is increased in current OC users, even with newer low-estrogen preparations.2 However, the absolute increase in stroke risk is expected to be small because incidence is very low in this population, conclude the researchers.
What is the take-home message for family planners? "There is an increased risk of stroke with OCs, but the absolute risk is so small that it probably should not affect most women’s decision making," says S. Claiborne Johnston, MD, MPH, UCSF assistant professor of neurology and senior author of the meta-analysis.
To determine the protective effects of sub-50 mcg pills, investigators interviewed 767 women ages 20 to 69 who had been diagnosed with epithelial ovarian cancer within the previous six months. The subjects were drawn from 39 hospitals in Pennsylvania, southern New Jersey, and Delaware. Also interviewed as controls were 1,367 women ages 20 to 69 who were selected primarily through random telephone calls within the same geographic areas as the subjects.
Contraceptive use, including type, frequency, and duration, was examined, as well as menstrual onset, regularity, and cessation; length and outcome of each pregnancy; and length of time breast-feeding. Interviewers obtained information on active ingredients and doses in the OCs used by women. To validate dose findings, researchers compared women who began using OCs before 1972, when high-dose pills dominated the market; between 1972 and 1980, when pills were moving to lower-dose formulations; and after 1980, when lower-dose pills became the dominant force in the marketplace.
Study results showed that the risk of ovarian cancer was reduced by an average of 40% for OC users, regardless of age at initiation. Amounts of estrogens and progestins in the pill formulations didn’t affect the degree of protection. Cancer protection began after a period of one to four years.
Those women who stopped taking the pill 30 years ago were protected to the same degree as those who stopped less than 10 years ago, results indicate. Body mass index, race, number of pregnancies, and age at first menstruation and at menopause did not affect the risk.
While research has indicated that OC use may reduce the risk of ovarian cancer in women with hereditary factors for the disease,3 further investigation is needed to evaluate the full benefit vs. risk, says Ness. "OCs are generally a wonderful form of contraception. They have, clearly, certain risks associated with them, but they are really very minimal from a population-based perspective."
UCSF researchers reviewed 73 investigations and chose 16 to perform their meta-analysis of the risk of ischemic stroke in OC users. The selected studies, conducted between 1960 and 1999, reflected different risk factors for stroke. The meta-analysis took into account possible weaknesses of the studies, including the account of risk factors, and attempted to compensate for them.
Results of the meta-analysis show a relative risk of 1.93 for women taking low-dose (sub-50 mcg) pills. The overall risk among all current users, which includes women taking various doses of the drug, more than doubled the risk of stroke to 2.75, with the risk rising to 4.53 in women taking high-dose estrogen contraceptives.
"What is interesting about the findings of this meta-analysis is that two recent U.S. studies failed to observed any increased stroke risk in OC users,"4-5 says Andrew Kaunitz, MD, professor and assistant chair in the obstetrics and gynecology department at the University of Florida Health Science Center/Jacksonville and director of menopause and gynecology services at the Medicus Women’s Diagnostic Center in Jacksonville.
U.S. clinicians’ practice patterns differ somewhat from those overseas when it comes to providing OCs, says Kaunitz. American clinicians prescribe OCs formulated with less than 50 mcg of estrogen, check blood pressure before and during OC use, and don’t prescribe OCs to women older than 35 who smoke. (Contraceptive Technology Update readers confirm this practice in the recent 2000 Contraception Survey, published in the September issue.)
"It is likely that these practice patterns explain why U.S. OC users, in contrast to their counterparts abroad, experience no elevated risk of stroke," Kaunitz notes.
References
1. Ness RB, Grisso JA, Klapper J, et al. Risk of ovarian cancer in relation to estrogen and progestin dose and use characteristics of oral contraceptives. SHARE Study Group. Steroid Hormones and Reproductions. Am J Epidemiol 2000; 152:233-241.
2. Gillum LA, Mamidipudi SK, Johnston SC. Ischemic stroke risk with oral contraceptives: A meta-analysis. JAMA 2000; 284:72-78.
3. Narod SA, Risch H, Moslehi R, et al. Oral contraceptives and the risk of hereditary ovarian cancer. N Engl J Med 1998; 339:424-428.
4. Petitti DB, Sidney S, Bernstein A, et al. Stroke in users of low-dose oral contraceptives. N Engl J Med 1996; 335:8-15.
5. Schwartz SM, Petitti DB, Siscovick DS, et al. Stroke and use of low-dose oral contraceptives in young women: A pooled analysis of two U.S. studies. Stroke 1998; 29:2,277-2,284.
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