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A prospective multicentre trial of the ovulation method of natural family planning. Pt. 2. The effectiveness phase.
Fertility and Sterility. 1981 Nov; 36(5):591-98.A 5 country prospective study was undertaken to determine the effectiveness of the ovulation method of natural family planning. 869 subjects of proven fertility from 5 centers (Auckland, Bangalore, Dublin, Manila, and San Miguel) entered the teaching phase of 3-6 cycles; 765 (88%) completed the phase. 725 subjects entered a 13-cycle effectiveness phase and contributed 7514 cycles of observation. The overall cumulative net probability of discontinuation for the effectiveness study after 13 cycles was 35.6%, 19.6% due to pregnancy. Pregnancy rates per 100 woman-years calculated using the modified Pearl index were as follows: conscious departure from the rules of the method, 15.4; inaccurate application of instructions, 3.5; method failure, 2.8; inadequate teaching, 0.4; and uncertain, 0.5. Cycle characteristics included: 1) average duration of the fertile period of 9.6 days, 2) mean of 13.5 days occurred from the mucus peak to the end of the cycle, 3) a mean of 15.4 days of abstinence was required, and 4) a mean of 13.1 days of intercourse was permitted. Almost all women were able to identify the fertile period by observing their cervical mucus but pregnancy rates ranged from 27.9 in Australia and 26.9 in Dublin to 12.8 in Manila. Continuation was relatively high ranging from 52% in Auckland to 74% in Bangalore.
In: Jeffcoate SL, ed. Ovulation: methods for its prediction and detection. Chichester, England, John Wiley, 1983. 33-47. (Current Topics in Reproductive Endocrinology Volume 3)This chapter reviews certain recognizable biological effects that occur due to the major changes in the circulating blood levels of estrogen and progesterone and discusses the ongoing use of these biological signals for the self detection of ovulation and the fertile phase of the cycle. These biological changes include the basal body temperature, changes in the cervix and its mucus secretion, mittelschmerz, and the menstrual cycle molimina. The calculation or calendar method is the oldest technique for determining the fertile period and followed the work of Ogino (1930) and Knaus (1933). The fertile phase of the cycle was identified from the records of the previous 6-12 menstrual cycles. The potential fertile period was then calculated on the following basis: define the shortest and the longest menstrual cycle over the preceding 6 and preferable 12 cycles; the 1st day of the potentially fertile phase is the longest cycle minus 11 days. For a women whose menstrual cycles have varied between 26-31 days, the potential fertile period would be days 8-20 of the cycle. The greatest weakness of the calendar calculation is that it depends on a prediction, based on the menstrual history, of what is likely to occur and not on what is actually taking place. Very rapid electronic thermometers are now available which offer considerable advantages over the clinical thermometer. The daily taking and charting of the basal body temperature (BBT) is the simplest and most widely used method for detecting ovulation. To overcome the drawbacks of the calendar method and the BBT method for identifying the fertile period, John and Evelyn Billings of Melbourne in the early 1970s developed the ovulation method. Self recognition of cervical mucus symptoms provides the woman with a simple means of detecting the fertile phase of her cycle and the likely time of ovulation. Individual cycle variation in the preovulatory duration of the symptoms limits the position of the prediction, yet the "peak" day correlates better with the time of ovulation than the shift in BBT. In addition to effects on cervical mucus, estrogen also changes the morphology of the cervix. The preovulatory rise in estrogensoftens the tissues of the cervix and opens the cervical os. The softened cervix and gaping os with a cascade of clear mucus is a sign of optimal estrogen response and of imminent ovulation. A World Health Organization (WHO) multicenter study of the ovulation method provided a substantial amount of information of the normal menstrual cycle of a large number of women of proven fertility in the age group 18-39 years whose cycles were not influenced by the use of hormonal or other contraceptive methods.