Susan Tew/Chris Kirchgaessner
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Two New Studies Find Wide Range of Effectiveness, Depending On
Method and User--Consistency of Correct Use Clearly Important
While most women using reversible contraceptives successfully prevent unplanned pregnancies, overall, some 9-12 percent become pregnant within the first 12 months of starting use, according to two analyses published in the March/April 1999 issue of The Alan Guttmacher Institute's (AGI's) bimonthly peer-reviewed journal, Family Planning Perspectives. The studies--one by AGI and the other by Princeton University researchers--together provide the most detailed portrait to date of the effectiveness of current contraceptive practices in the United States. They include estimates of contraceptive efficacy by method and by user characteristics, such as age, race/ethnicity, income, religion and marital/cohabitation status.Both analyses are based on data from the 1995 National Survey of Family Growth (NSFG), a nationally representative survey of U.S. women of reproductive age, conducted by the U.S. National Center for Health Statistics. Comparison of the two reveals broad similarities and some distinct differences, largely due to the researcher's differing perspectives on abortion data in the NSFG. Whereas the AGI researchers correct for the underreporting of abortion by women in the NSFG in calculating failure rates--overall, abortions were underreported in the 1995 survey by more than 40%--the Princeton University researchers prefer to rely on the level of abortion reported in the survey, asserting that correcting for underreporting probably results in overestimates of contraceptive failure rates. Since underreporting of abortion varies by contraceptive method and user (and is particularly high among women known to experience high levels of unintended pregnancy), the two analyses reveal somewhat different groups of women with a high likelihood of accidental pregnancy. They also show somewhat different failure rates, particularly for some methods.
Both analyses find that in actual practice, some methods carry a lower risk of failure than others: Long-term methods requiring no ongoing effort by the user--the hormonal implant, the injectable and the IUD--have a very low failure rate. However, among methods that require either daily or episodic action by the user, some--the pill, the diaphragm and the condom--have slightly higher, medium-level failure rates, and others--spermicides, withdrawal and periodic abstinence-- have considerably higher rates. Both studies show that failure rates representing the actual experience of users ("typical use") are considerably higher than the efficacy that might be achieved if all methods were always used correctly and consistently ("perfect use"). Both find that on average, although users have about a one in 10 likelihood of experiencing pregnancy, levels of failure vary widely by personal characteristics of the user and by type of method. Finally, both agree that low-income women, Hispanic women and (at least for some methods) younger women are among the groups most vulnerable to an accidental pregnancy; however, the analyses disagree about the effect of race.
"Contraceptive Failure Rates: New Estimates from the 1995 National Survey of Family Growth," by Haishan Fu, Jacqueline E. Darroch, Taylor Haas and Nalini Ranjit of AGI, asserts that failure rates determined straight from the NSFG are underestimated because six in 10 unintended pregnancies resulting from contraceptive failure end in abortion and women do not report many of these abortions in the survey. In addition to young, low-income, Hispanic women, according to the AGI analysis, black women and unmarried women (particularly those living with their sexual partners) are among the groups with a high likelihood of contraceptive failure during the first year of typical use of a method.
"Contraceptive Failure, Method-Related Discontinuation and Resumption of Use: Results from the 1995 National Survey of Family Growth," by James Trussell and Barbara Vaughan of Princeton University, calculates failure rates straight from the NSFG, arguing that women in abortion clinics and women in personal interviews for the NSFG overreport use of a contraceptive method at the time of a conception.
The Trussell/Vaughan analysis breaks new ground by examining how frequently women discontinue--and resume--using a contraceptive. A typical woman discontinues using a method nearly 10 times over the course of her reproductive lifetime, and experiences about two contraceptive failures. Three in 10 (31%) women discontinue method use within six months, and four in 10 (44%) do so within 12 months. However, within one month of discontinuation seven in 10 (68%) resume contraceptive use, and within three months, eight in 10 (76%) do so. The researchers find that not only do low-income women have a much higher risk of contraceptive failure than other women, they also are less likely than other women to resume contraceptive use after discontinuing a reversible method.
The March/April issue of Family Planning Perspectives features another study examining contraceptive practices among U.S. women:
"Measuring Contraceptive Use Patterns Among Teenage and Adult Women," by Dana Glei of Princeton University, suggests that a key to understanding women's risk of unplanned pregnancy is examining their long-term contraceptive use (for example, over the past year), as opposed to use at a given point in time (such as, at first or last intercourse). The analysis, also based on the 1995 NSFG, finds that nine in 10 women at risk of unplanned pregnancy use a contraceptive method steadily over the course of a year. However, teenagers, women who are not married or cohabiting, and those who have recently experienced coercive sex are much less likely than others to report uninterrupted use of a contraceptive method.
Glei's findings point to the influence of personal and behavioral factors on the consistency of contraceptive use and therefore on the risk of unplanned pregnancy. The researcher notes that efforts to reduce unintended pregnancy will have the greatest impact if focused on supporting contraceptive use among both women at high risk of unplanned pregnancy who are not using a method and those who are using contraceptives sporadically (because of their moderately high risk of pregnancy combined with their large numbers).
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To contact James Trussell, Barbara Vaughan or Dana Glei, please call:
Office of Population Research, Princeton University: 609/258-4810
The Alan Guttmacher Institute is a nonprofit organization focused on reproductive health research, policy analysis and public education, with offices in New York City and Washington, D.C.
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