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The Rhythm Method, also known as the Calendar Method or the Knaus-Ogino Method (named after Hermann Knaus and Kyusaku Ogino), is a method of natural birth control that involves counting days of a woman's menstrual cycle in order to achieve or avoid pregnancy.
A recently developed variant of the Rhythm Method is known as the Standard Days Method. Developed by Georgetown University's Institute for Reproductive Health, the Standard Days Method has a simpler rule set and is more effective than Rhythm. A product, called CycleBeads, was developed along side the method to help a user keep track of high and low fertility points during a menstrual cycle.
The Rhythm Method is sometimes considered a form of fertility awareness. However, modern techniques of fertility awareness generally rely on several physiological signs of fertility, rather than a simple counting of days. Because of its lower accuracy, many fertility awareness teachers consider calendar rhythm to have been obsolete for at least 20 years. At one time, the Rhythm Method was sanctioned as an acceptable form of natural family planning by the Catholic Church, although, as in the fertility awareness community, more modern methods are being advocated by the church today.
Description and effectiveness
Most menstrual cycles have several days at the beginning that are infertile (pre-ovulatory infertility), a period of fertility, and then several days just before the next menstruation that are infertile (post-ovulatory infertility). The first day of red bleeding is considered day one of the menstrual cycle. The formula for Calendar Rhythm requires the woman to know the length of her menstrual cycles.
To find the length of the pre-ovulatory infertile phase, nineteen (19) is subtracted from the length of the woman's shortest cycle. To find the start of the post-ovulatory infertile phase, ten (10) is subtracted from the length of the woman's longest cycle.Kippley, John and Sheila Kippley. The Art of Natural Family Planning. The Couple to Couple League, Cincinnati, OH: 1996. p.154. ISBN 0926412132
A woman whose menstrual cycles ranged in length from 30 to 36 days would, according to the Rhythm Method, be infertile the first 11 days of her cycle (30-19=11), be fertile on days 12-25, and resume infertility on day 26 (36-10=26). When used to avoid pregnancy, the Rhythm Method has a perfect-use failure rate of 9% per year.
The Standard Days Method may only be used by women whose cycles are always between 26 and 32 days in length. In this system, days 1-7 of a woman's menstrual cycle are considered infertile. Days 8-19 are considered fertile. Infertility resumes beginning on day 20. When used to avoid pregnancy, the Standard Days Method has a perfect-use failure rate of 5% per year.
Imperfect use of the Rhythm Method would consist of not correctly tracking the length of the woman's cycles, thus using the wrong numbers in the formula, or of having intercourse on an identified fertile day. Imperfect use is fairly common, and the actual failure rate of the Rhythm Method is 25% per year.James Trussell et al.Contraceptive effectiveness rates. Contraceptive Technology — 18th Edition, New York: Ardent Media. On-press, 2000.
Reasons for high failure rate
The Rhythm Method formula makes several assumptions that are not always true.
The postovulatory (luteal) phase has a normal length of 12 to 16 daysWeschler, Toni. Taking Charge of Your Fertility. HarperCollins, New York: 2002. p.48 ISBN 0060394064, and the Rhythm Method formula assumes all women have luteal phase lengths within this range. However, many women have shorter luteal phases, and a few have longer luteal phasesKippley, p.111. For these women, the Rhythm Method formula incorrectly identifies a few fertile days as being in the infertile period.
The Rhythm Method uses records of past menstrual cycles to predict the length of future cycles. However, the length of the pre-ovulatory phase can vary significantly, depending on the woman's typical cycle length, stress factors, medication, illness, menopause, breastfeeding, and whether she is just coming off hormonal contraception. If a woman with previously regular cycles has a delayed ovulation due to one of these factors, she will still be fertile when the Rhythm Method tells her she is in the post-ovulatory infertile phase. If she has an unusually early ovulation, the Rhythm Method will indicate she is still in the pre-ovulatory infertile phase when she has actually become fertile.
Finally, the Rhythm Method assumes that all bleeding is true menstruation. However, mid-cycle or annovulatory bleeding can be caused by a number of factors. Incorrectly identifying bleeding as menstruation will cause the Rhythm Method's calculations to be incorrect.
History
Precursors to the Rhythm Method were developed in the mid-nineteenth century. p. 307. In 1905 Theodoor Hendrik Van de Velde, a Dutch gynecologist, showed that women only ovulate once per menstrual cycle. In 1924, Kyusaku Ogino in Japan developed a formula for the Rhythm Method. The formula was confirmed and improved by Hermann Knaus in Austria in 1928.
The 1930 encyclical Casti Connubii by Pope Pius XI was controversially interpreted to allow moral use of the Rhythm Method, and in 1932 a Catholic physician published a book titled The Rhythm of Sterility and Fertility in Women describing the method. The 1930s also saw the first U.S. Rhythm Clinic (founded by John Rock) to teach the method to Catholic couples. However, it was not until Pope Pius XII's 1951 addresses (English translation entitled Moral Questions Affecting Married Life) that the Catholic Church explicitly accepted use of the Rhythm Method.
Humanae Vitae, published in 1968 by Pope Paul VI, addressed a pastoral directive to scientists: "It is supremely desirable... that medical science should by the study of natural rhythms succeed in determining a sufficiently secure basis for the chaste limitation of offspring." This is interpreted as favoring the then-new, more reliable fertility awareness methods over the Rhythm Method.
References
"Rhythm Method"