THE NATURAL REGULATION OF FERTILITY
Many couples throughout the world choose to rely on natural methods for family planning; for the postponement of a first pregnancy, for spacing the intervals between their children, to avoid further pregnancies, or for all of these purposes. Some couples may prefer to avoid the use of artificial methods until after the birth of their first child, some may find the use of artificial methods unsatisfactory because of side effects, some are motivated by religious considerations. Whatever the reason for their adoption by couples, natural methods are established in almost all communities, and are extensively used in some.
The methods of natural family planning (NFP) rely for their effectiveness on the recognition of the time during the menstrual cycle when the woman will be fertile, and the avoidance of sexual intercourse during this time. The methods are commonly referred to as being based upon periodic abstinence. An important exception to this is the infertility associated with breast-feeding, a natural method of fertility regulation that does not depend upon abstinence from sexual intercourse.
Abstinence, whether periodic or terminal, has been used for centuries as a means of regulating fertility in many societies. However, attempts to define an infertile (safe) period during the menstrual cycle, as against a fertile (unsafe) period, were forced to wait until there was some elucidation of the relationship between the ovarian cycle and the menstrual cycle. Thus, although the biphasic fluctuation in body temperature in women of reproductive age was recognized in 1868 it was not until 1928 that the shift from lower to higher temperature was associated with ovulation and corpus luteum activity. Subsequently it was suggested that this shift in temperature might be used as a basis for the practice of periodic abstinence. Formulae for calculation of the fertile phase of the cycle based on the length of previous menstrual cycles were not produced until the 1930s, and the use of mucus signs to determine the fertile period was not introduced until the 1960s.
The methods of NFP, therefore, are essentially modern and depend on our understanding of the relationship between physiological symptoms and signs, or biochemical or biophysical signals, and ovulation (11,12,15,16). These, combined with estimates of the fertile lifespan of spermatozoa in the female genital tract and ova following ovulation, form the basis of the four commonly used NFP methods. Useful collections of papers can be found in the volumes edited by Queenan et al. (6) and Van Look and Mancuso (10).
The calendar method (syn. rhythm method)
As its synonym implies, this method is based on the assumption that, for each woman, there is a rhythmic pattern of menstruation and ovulation that can be identified by keeping a careful record of the dates of menstruation. A second assumption is that ovulation occurs 14 days before the onset of the next menstruation. The calendar method is the most commonly used of the natural methods.
To be used effectively a record should be kept for at least six menstrual cycles. The fertile period is then defined by a set of rules, for example: the length of the shortest cycle less 18 days marking the start of the fertile period and the length of the longest cycle less 11 days marking the end of the fertile period. The interval, so defined, is modified according to the length of subsequent cycles.
It is believed that the great majority of couples who rely on this method do not follow such a methodical approach. Many couples learn of the method from their peers and follow simple rules such as avoiding intercourse between days 7 and 21 following the onset of menstruation. Such couples often have scant knowledge of the underlying physiology. In some populations barrier methods are used during the calculated, or assumed, fertile period.
The ovulation method (syn. cervical-mucus method, Billings method)
Introduced only in the 1960s, this method relies on self-examination by the woman for the detection of the quantity, and evaluation of the quality, of mucus produced by the glands of the cervix during the latter part of the follicular phase of the cycle, leading up to ovulation.
Following the cessation of menstruation there are a variable number of days, characterized as " dry ", when no mucus can be detected in the vagina on self-examination. Following these few days, there is an increasingly detectable amount of mucus, the character of which is " sticky ". After another few days there is a significant increase in the volume of mucus which becomes more watery and " slippery ", and also has the property of " spinnbarkeit ", or " stretchiness ". The peak amount of slippery mucus occurs at, or just before, ovulation. The end of the fertile period is calculated from the day on which this peak volume is detected.
Couples are advised to practice abstinence during menstruation, on every second of the " dry " days, during the whole time from the day when sticky mucus is first detected until four days after the day of peak, slippery mucus volume.
The method requires to be taught, particularly self-examination for evaluation of the volume and quality of mucus which should be done daily and the result entered on a specially designed chart. However, the evidence is that women are able to learn the method quite rapidly. In a large study supported by WHO in five countries, 94% of women were able to detect the changes in cervical mucus after three teaching cycles, and 91% were rated as having good or excellent understanding of the method after just one teaching cycle (13).
A simplified version of the ovulation method, called the modified mucus method (MMM), has been developed and is in use in some developing countries. This method has less strict rules for abstinence than the ovulation method and relies more on the identification of slippery mucus alone. Because women using MMM do not need to fill in charts of mucus patterns it is claimed that this renders the method better suited for use by illiterate couples.
Basal body temperature (BBT) method (syn. temperature method)
In a normal, ovulatory cycle the temperature of the body measured on awakening, called the basal state, rises by 0.2°C to 0.5°C during two or three days following ovulation. The rise is defined as one in which three consecutive daily temperatures are at least 0.2°C higher than the six daily temperatures preceding the shift. This rise reflects the secretion of progesterone from the corpus luteum. For the remainder of the cycle, until a few days before the onset of menstruation, the temperature stays at this higher level and marks the infertile phase of the cycle. Used in this way the BBT method, until very recently, has been the most quantitative method for the detection of ovulation in the home. BBT measurements require the use of a special thermometer. In recent years a number of digital thermometers capable of indicating the fertile and infertile days of the cycle based on BBT changes and information about the lengths of past cycles stored in the device’s memory have been marketed.
Couples are advised to avoid intercourse from the onset of menstruation until there have been three days of recorded, higher temperature.
Among NFP methods the BBT method, used by itself, is the most demanding for the couple as it imposes the longest duration of abstinence, often between 14 and 21 days; for this reason it is rarely used alone.
This method combines features of the ovulation method with the BBT method and in addition may include other physical signs or symptoms detected by self-examination. These additional signs include the position of the cervix relative to the pelvis, the degree of dilatation of the external cervical os, and the occurrence of mid-cycle abdominal discomfort (mittelschmerz) or mid-cycle bleeding or spotting.
The symptothermal method, in effect, uses the guidelines of the ovulation method to determine the onset of the fertile period and the guidelines of the BBT method to determine its end. Used in this way the method reduces considerably the number of days of abstinence required by the BBT method alone. However, measurement and charting of all the above information is more demanding than either the ovulation or BBT methods alone. Despite the demands made, at least in the early stages of use, many women become very adept at recognizing the signs and symptoms of impending ovulation, and those with regular cycles can often reduce the period of abstinence without seriously risking pregnancy.
The ovulation and sympto-thermal methods also can be helpful in achieving pregnancy, and thus some knowledge of their basis can be useful in advising couples who wish to conceive but who do not fall within a group requiring full infertility investigation.
Efficacy of natural family planning methods
There have been few, objective, scientifically valid studies of the efficacy of the various NFP methods for avoiding pregnancy. The most extensive study of any method was the World Health Organization’s multicentre, cross-cultural study of the ovulation method to which 869 couples were recruited and 725 couples entered the 13 cycle effectiveness phase (13,14,17,18).
There were 130 pregnancies during the effectiveness phase, the majority of which resulted from breaches of the rules for use of the method. The life-table pregnancy rate for the effectiveness phase was 19.6 percent but the true method failure rate was calculated to be 2.8/100 women years (1300 cycles) during this phase of the study.
A further analysis of the data from the WHO study (9) showed that the probability of pregnancy during the first year of perfect use of the method was 3.1 percent (method failure). The probability of pregnancy if the method was used imperfectly was 86.4 percent at one year (user failure). This latter figure is similar to the expected pregnancy rate when no family planning method is used.
Breaking any of the three most crucial rules—no intercourse during mucus days, within three days after the peak mucus day or during times of stress—resulted in a 28 percent risk of conceiving in that cycle.
For the other NFP methods there are no good data on sufficient numbers of couples followed over time in a systematic way. The studies that have been published suggest that the symptothermal method has an efficacy similar to, if not slightly better than, that of the ovulation method and that BBT used alone is less effective than either of these with a pregnancy rate approaching 22 percent in the first year of use. A study in Indonesia of three variations of periodic abstinence, the ovulation method, MMM, and a local variation of fertile mucus recognition (8) yielded one-year life-table unplanned pregnancy rates of 2.5 per 100 women for the ovulation method, 10.3 per 100 women for MMM, and 11.5 per 100 women for the local method.
For the calendar method, which is by far the most widely practiced, there is almost no information on efficacy. A study in the Philippines (5), a country in which 99 percent of NFP users use a calendar method, suggested that the risk of pregnancy was about 3 percent per cycle. Seventy one percent of those who had experienced failure of the calendar method blamed their own behaviour, suggesting that the true, method failure rate is lower than that quoted.
Breast-feeding and birth spacing
Although the benefits of breast-feeding to the infant have always been known and widely promoted, it is only recently that family planning scientists have taken an interest in the birth-spacing effects of prolonged lactation. This interest resulted in a consensus meeting in 1987 that produced the guiding principle that women who fully, or nearly fully, breast-feed, and who remain amenorrhoeic have a less than two percent chance of becoming pregnant in the first six months following delivery. This general statement has become known as the Bellagio consensus (3).
Several studies have validated the Bellagio consensus, and some have suggested that the chance of becoming pregnant, when the other conditions are fulfilled, may be less than one percent (4,7). A birth-spacing method, the lactational amenorrhea method (LAM), based on the Bellagio consensus (4), has been introduced into a number of family planning programmes where it has been shown to improve the acceptance of conventional contraceptive methods at the end of six months or the resumption of menses, and also to improve the duration for which women fully, or nearly fully, breast-feed their infants.
The precise biological mechanisms responsible for the suppression of ovulation during full breast-feeding are incompletely understood. On the basis of present knowledge it is not possible to predict, by any existing method, which women will continue in amenorrhea for a long period and which will resume menstruation comparatively early after delivery. The only thing that is known with any certainty is that, for any one woman, the duration of lactational amenorrhea following previous pregnancies is highly predictive for the duration of lactational amenorrhea following a present pregnancy (2).
Edited by Aldo Campana,