The Rules of the Billings Ovulation Method

Early Day Rules for Pregnancy Avoidance

For pregnancy avoidance the BOM has four rules, three Early Day Rules and the Peak rule. The Early Day Rules are formulated to give the earliest possible prediction of ovulation to allow for the longest possible sperm survivals. As the BOM relies on sensation at the vulva, and time is required for the discharges to drain into the vulval area, time by the woman in the upright position is required for accurate identification. Furthermore, seminal fluid obscures the observations and needs to be absorbed or drained away before accurate observations can be made. Therefore, to achieve these two requirements for all the types of ovarian activity the Early Day Rules state the following:

1. Times of the full menstrual flow or other types of bleeding are not available for intercourse since these obscure the discharge symptoms . Intercourse may be resumed towards the end of menstrual bleeding (that is bleeding following a distinct PC and Peak day) when it is light or spotting is occurring, provided that the fertility symptoms are not being obscured.
2. When a BIP is identified, alternate evenings are available for intercourse.
3. When a change from a BIP discharge or bleeding is observed the couple waits without intercourse. If the same BIP returns, intercourse may be resumed on the fourth evening after the return of the BIP. This is the wait and see, one, two, three rule.

More usually, the change from a BIP is progressive with the discharge changing daily in characteristics which are becoming increasingly fertile, slipperiness being the most important final quality. The phase of possible fertility begins with the first change from the BIP (the ER) and from then on a time of no genital contact is observed. In short cycles, there may be insufficient time after bleeding to identify a BIP before a follicle begins to develop, in which case no pre-ovulatory days are available for intercourse. Occasionally during breast-feeding or approach of menopause, a BIP may change to another BIP with more fertile characteristics. In this case a wait-and-see period of 2 weeks is required before assuming that the change is in fact to a new BIP before resuming intercourse. The woman notes that the change is not progressive ("not going anywhere"). When no PC providing recognition of the Peak day is observed, the woman continues to apply the Early Day Rules.

The Peak Rule for Pregnancy Avoidance

The Peak day is the last day that mucus with fertile characteristics (slippery) is felt before the progesterone change (PC). It is thus determined retrospectively by this change. The Peak rule states that intercourse may be resumed on the fourth morning after the Peak day. All times from then until the next menstruation are available for intercourse. The Peak rule provides a well-tested minimum safety margin between the resumption of intercourse at the beginning of the post-ovulatory infertile phase and the Peak day, which is the day of maximum fertility.

Pregnancy Achievement

For pregnancy achievement, the couple aims to have intercourse on the Peak day, the day of peak fertility. However, the Peak day is identified in retrospect by the progesterone change, and, furthermore, intercourse on the Peak day produces seminal fluid which obscures this change. Therefore, in these circumstances, the Peak day cannot be determined with certainty. The best that can be done is to have intercourse when the discharges seem to be maximally fertile, namely when a slippery sensation is felt at the vulva. This is understood more clearly by those women who have had previous experience with their symptoms in avoiding pregnancy. When the timing is correct and no pregnancy results, the couple usually begin to despair and want to know the reason. Fertility is one of the most variable phenomena in human activity and is the sum total of both partners' fertility. The most fertile couples are those where the man produces the most robust and numerous sperm and the woman provides the longest and best cervical mucus production to nurture them. Such couples conceive following almost any act of intercourse during the fertile phase with a pregnancy rate of about 70% per act of intercourse during the fertile phase. At the other end of the spectrum, the combined sperm/mucus interaction of the couple may be so poor that the sperm have fertilizing ability only for the few hours of optimum mucus production close to ovulation. These couples are self selecting and are the main group presenting with infertility. They have a probability of conception of about 10% per cycle and therefore, without accurate timing of intercourse, it would take several years of trying before the majority had achieved pregnancy. When conception has not occurred within say six successfully timed cycles using the BOM symptoms, it is worth trying even more accurate methods of timing ovulation such as the LH kits or the Home Ovarian Monitor. Failing to conceive when wanted is stressful and therefore favours infertility. It should be remembered that, apart from a few conditions such as blocked fallopian tubes, absent sperm and continued anovulation, most couples will conceive eventually without help. However, the modern expectation is one of immediate results and the main function of assisted reproduction techniques is therefore to shorten the waiting time for conception.

It is seen that the rules of the BOM cope effectively with all the types of ovarian activity yet discovered. It should be emphasized that the BOM recognizes only one type of cycle, that is the ovulatory cycle in which a PC providing calculation of a Peak day is observed and which therefore ends with menstruation. This includes the fully fertile ovulatory cycle and the infertile ovulatory cycles with deficient or short luteal phases. The first day of menstruation is counted as the first day of the cycle. Bleeding which occurs without a Peak day preceding it is not counted as the end of a cycle but is considered to be still the early part of an ovulatory (possibly fertile) cycle which will follow it. Thus the emphasis in the BOM is on cyclic fertility. This contrasts with other definitions which refer to cycles of bleeding or cycles of ovarian activity. Thus it is possible to have ovulatory or anovulatory cycles of bleeding or of ovarian activity. In our work in measuring hormone production the term "cycle" has been applied to the growth and regression of follicles within the ovaries whether they ovulate or not by measuring the rise and fall in oestrogen and progesterone production. Thus this application of the term "cycle" refers to cyclic ovarian activity which is related to but not identical with cyclic fertility. The distinction is made by the BOM to steer women away from the old concept of concentrating on the bleeding symptom, which is uninformative, and making them concentrate on the fertility symptoms which are really what matter. Furthermore, the BOM concentrates on the patterns of discharges which reflect the underlying dynamic ovarian events associated with fertility and infertility rather than on the detailed descriptions of the discharges which vary from woman to woman.

Research Effort

The BOM was developed only after a complete appraisal of the NFP methods which were available in the late 1950s, including the rhythm method and the use of the BBT, and finding that none could hope to match the newly developed contraceptive pill in efficacy and acceptability. The above understanding of the application of the vaginal discharge symptoms to fertility awareness, as applied in the BOM, has been arrived at after more than 30 years of intensive research which has had little support from granting bodies. Firstly, the observations were made on the women themselves as the rules were developed and used in practice. Some women planning pregnancy volunteered to test their fertility on days relative to the Peak day and all pregnancies were carefully assessed as to the timing of the intercourse which caused them. Secondly, Professor Erik Odeblad, in Sweden, has done years of pioneering work on typing the cervical mucus and determining the significance of each type in the fertility process. Thirdly, the above study of the relationship between the mucus changes, ovarian activity and fertility involved approximately 750,000 hormone assays for both pregnancy avoidance and achievement, countless ultrasound observations and the monitored use of FSH, LH (HCG) and clomiphene in the induction of ovulation. Such a large study has been necessary because approximately 90% of ovarian cycles are ovulatory and the remaining 10% are distributed among the other variants. The ovulatory cycle has been extensively studied by many workers but the other variants have been largely overlooked. This is because these other variants are not predictable and large numbers of cycles needed to be studied so that the variants could be documented and their mechanism, frequency and impact on the mucus symptoms and fertility determined. To expedite the study, the search was concentrated on those times when these cycle variants are most common, namely menarche, stress, infertility, postpartum, breast-feeding and approach of menopause. Because NFP operates with an intact and functioning reproductive system, it has been important to study all the types of ovarian activity that occur in women so that the times of possible fertility and absolute infertility can be recognized with certainty and the full potential of the method can be realized. The work involved in the overall development of modem methods of NFP has necessarily been far more extensive and demanding than that required for other methods of family planning, all of which are designed to interfere predictably in the intricate processes of reproduction and the main research requirement has been to determine efficacy, acceptability and the minimization of deleterious side effects. It should be stated that much of this research in NFP has been conducted in parallel with research in assisted reproduction and that each field has made important contributions to the other. In fact, it is unlikely that the full potential of either field is possible without the information provided by the other. This is the direction of further research.

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