Trussell, J., & Grummer-Strawn, L. (1990). Contraceptive failure of the ovulation method of periodic abstinence. Family Planning Perspectives, 22(2), 65-75. https://doi.org/10.2307/2135511
Trussell J, Grummer-Strawn L. Contraceptive failure of the ovulation method of periodic abstinence. Fam Plann Perspect. 1990;22(2):65-75. doi:10.2307/2135511
Trussell, James, and Laurence Grummer-Strawn. "Contraceptive failure of the ovulation method of periodic abstinence." Family Planning Perspectives, vol. 22, no. 2, 1990, pp. 65-75.
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The authors say the ovulation method is very effective if used perfectly, but extremely unforgiving of imperfect use. Among women in a World Health Organization trial, the first-year chance of pregnancy was 3.1 percent with perfect use. With imperfect use it was 86.4 percent.
Key Findings
The authors report a 3.1 percent chance of pregnancy in the first year of perfect use, which they call method failure.
The authors report an 86.4 percent chance of pregnancy in the first year of imperfect use, which they call user failure.
The authors say the pregnancy risk is highest when a woman breaks any of three rules: mucus days, the three days after peak fecundity, or times of stress.
The authors report a 28 percent risk of pregnancy per cycle when the most serious rules are broken.
Interpretation
The source is a 1990 journal abstract, so only the authors' summary is available here. The data come from a clinical trial in which couples volunteered. The authors argue that earlier failure estimates for every contraceptive method ran too low and present their figures as the first correct ones. They also argue that typical couples are likely to follow the rules less closely than trial volunteers. The abstract gives no participant numbers or confidence intervals.
RRM Context
The paper evaluates one method of cycle charting as a contraceptive. RRM uses charting mainly to read the cycle, find root causes, and guide evaluation before treatment. The abstract reports nothing about those uses. Its figures describe one trial population and one set of method rules.
Our editorial summary of this paper, not the article's abstract.
Abstract
Previously published estimates of probabilities of method and user failure for all contraceptive methods suffer from a serious methodological error and are biased downward, with the extent of bias unknown. Data from a World Health Organization clinical trial of the ovulation method of periodic abstinence were used to provide the first correctly calculated measures of method and user efficacy and to determine the characteristics that distinguish women who consciously take risks from those who do not. Probabilities of pregnancy during the first year are 3.1 percent during perfect use (method failure) and 86.4 percent during imperfect use (user failure). Thus, if used perfectly, the ovulation method is very effective. However, it is extremely unforgiving of imperfect use. Because perfect compliance is difficult for many couples who desire intercourse when it is forbidden by ovulation method rules, and because the risk of pregnancy during imperfect use is so great, the ovulation method cannot be considered an ideal contraceptive method for the typical couple, who are likely to be less compliant than couples who volunteer for a clinical trial. The probability of an accidental pregnancy is greatest when any of the three most serious rules--no intercourse during mucus days, within three days after the day of peak fecundity or during times of stress--are broken. Those who have a poor attitude toward the rules are more likely to take risks, including serious risks. Those who get away with taking a risk (i.e., do not get pregnant) are very likely to take risks again. Because breaking the most serious rules entails a 28 percent risk of pregnancy per cycle, those likely to take risks should be counseled about the probable consequences.
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