Calendar-based contraceptive methods

Calendar-based methods are various methods of estimating a woman's likelihood of fertility, based on a record of the length of previous menstrual cycles. Various methods are known as the Knaus–Ogino method and the rhythm method. The standard days method is also considered a calendar-based method, because when using it, a woman tracks the days of her menstrual cycle without observing her physical fertility signs. The standard days method is based on a fixed formula taking into consideration the timing of ovulation, the functional life of the sperm and the ovum, and the resulting likelihood of pregnancy on particular days of the menstrual cycle. These methods may be used to achieve pregnancy by timing unprotected intercourse for days identified as fertile, or to avoid pregnancy by avoiding unprotected intercourse during fertile days.

The first formalized calendar-based method was developed in 1930 by John Smulders, a Catholic physician from the Netherlands. It was based on knowledge of the menstrual cycle. This method was independently discovered by Hermann Knaus (Austria), and Kyusaku Ogino (Japan). This system was a main form of birth control available to Catholic couples for several decades, until the popularization of symptoms-based fertility awareness methods. A new development in calendar-based methods occurred in 2002, when Georgetown University introduced the Standard Days Method. The Standard Days Method is promoted in conjunction with a product called CycleBeads, a ring of colored beads which are meant to help the user keep track of her fertile and non-fertile days.

Terminology

While the terms rhythm method and fertility awareness are not synonymous, some sources do treat them as such.

More effective than calendar-based methods, systems of fertility awareness that track basal body temperature, cervical mucus, or both, are known as symptoms-based methods. Teachers of symptoms-based methods take care to distance their systems from the poor reputation of the rhythm method.[3] Many consider the rhythm method to have been obsolete for at least 20 years,^[4] and some even exclude calendar-based methods from their definition of fertility awareness.^[5]

Some sources may treat the terms rhythm method and natural family planning as synonymous.

In 1905 Theodoor Hendrik van de Velde, a Dutch gynecologist, showed that women only ovulate once per menstrual cycle.^[12] In the 1920s, Kyusaku Ogino, a Japanese gynecologist, and Hermann Knaus, from Austria, working independently, each made the discovery that ovulation occurs about fourteen days before the next menstrual period.^[13] Ogino used his discovery to develop a formula for use in aiding infertile women to time intercourse to achieve pregnancy.

In 1930, Johannes Smulders, a

In the first half of the 20th century, most users of the rhythm method were Catholic; they were following their church's teaching that all other methods of birth control were sinful. In 1968 the encyclical Humanae vitae included the statement, "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 symptoms-based fertility awareness methods over the rhythm method. Currently, many fertility awareness teachers consider the rhythm method to have been obsolete for at least 20 years.^[4]

New attention was drawn to calendar-based methods in 2002, when the Institute for Reproductive Health at Georgetown University introduced the Standard Days Method. Designed to be simpler to teach and use than the older rhythm method, the Standard Days Method is being successfully integrated into family planning programs worldwide.

Types 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. To use these methods, a woman is required to know the length of her menstrual cycles.

Imperfect use of calendar-based methods would consist of not correctly tracking the length of the woman's cycles, thus using the wrong numbers in the formula, or of having unprotected intercourse on an identified fertile day. The discipline required to keep accurate records of menstrual cycles, and to abstain from unprotected intercourse, makes imperfect use fairly common. The typical-use failure rate of calendar-based methods is 25% per year.^[15]

Rhythm method (Knaus–Ogino method)

To find the estimated length of the pre-ovulatory infertile phase, eighteen (18) is subtracted from the length of the woman's shortest cycle. To find the estimated start of the post-ovulatory infertile phase, eleven (11) is subtracted from the length of the woman's longest cycle.^[16] A woman whose menstrual cycles ranged in length from 30 to 36 days would be estimated to be infertile for the first 11 days of her cycle (30-19=11), to be fertile on days 12–25, and to resume infertility on day 26 (36-10=26). When used to avoid pregnancy, such fertility awareness-based methods have a typical-use failure rate of 25% per year.^[15]

Standard days method

Developed at Georgetown University's Institute for Reproductive Health, the standard days method has a simpler rule set and is more effective than the rhythm method.^[15][17] A product called CycleBeads was developed alongside the method to help the user keep track of estimated high and low fertility points during her menstrual cycle. The standard days method may only be used by women whose cycles are usually between 26 and 32 days in length; it is estimated that between 50% and 60% of women of reproductive age satisfy this condition.^[18] In this system:

• Days 1–7 of a woman's menstrual cycle are considered infertile
• Days 8–19 are considered fertile; considered unsafe for unprotected intercourse
• Day 20 through the end of the cycle are considered infertile.

When used to avoid pregnancy, the standard days method has been estimated^[19] to have perfect-use efficacy of 95% and typical-use efficacy of 88%.^[17][18] These figures are based on a 2002 study in Bolivia, Peru, and the Philippines of women of reproductive age having menstrual cycles between 26 and 32 days,^{[17][20]: 505} and on a 2014 study in Turkey.^[21] However, other researchers have criticized the methodology of the first study, have stated that the 95% figure has been presented to the public in misleading ways, and have argued that the true efficacy figures are likely to be much lower.^[22]

Software-based systems

Several web-based implementations of the cycle method exist, as well as mobile apps such as Natural Cycles.^[23]

Advantages

The Standard Days method (SDM) is increasingly being introduced as part of family planning programs in developing countries. The method is satisfactory for many women and men.^[24][25] The low cost of the method may also enable it to play a useful role in countries that lack funding to provide other methods of birth control.^[26]

Potential concerns

Failure rate

One concern related to the use of calendar-based methods is their relatively high failure rate, compared to other methods of birth control. Even when used perfectly, calendar-based methods, especially the rhythm method, result in a high pregnancy rate among couples intending to avoid pregnancy. Of commonly known methods of birth control, only the cervical cap and contraceptive sponge have comparably high failure rates. This lower level of reliability of calendar-based methods is because their formulas make several assumptions that are not always true.^[16]

The postovulatory (luteal) phase has a normal length of 12 to 16 days,^[27] 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 phases.^[28] For these women, the rhythm method formula incorrectly identifies a few fertile days as being in the infertile period.^[16]

Calendar-based methods use 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 method tells her she is in the post-ovulatory infertile phase. If she has an unusually early ovulation, calendar-based methods will indicate she is still in the pre-ovulatory infertile phase when she has actually become fertile.^[16]

Finally, calendar-based methods assume that all bleeding is true menstruation. However, mid-cycle or

It has been suggested that pregnancies resulting from failures of periodic abstinence methods are at increased risk of miscarriage and birth defects due to aged gametes at the time of conception.[30] Other research suggests that timing of conception has no effect on miscarriage rates,^[31] low birth weight, or preterm delivery.^[32]

Destruction of fertilized eggs

Luc Bovens has suggested that unprotected intercourse in the infertile periods of the menstrual cycle may still result in conceptions, but create zygotes incapable of implanting.^[33] Bovens maintains that, if one defines abortion to include any destruction of fertilized eggs, then the use of the rhythm method probably results in a large number of abortions.

References