The deficiencies of these methods led to a study of the activity of the cervix of the uterus during the cycle and to the discovery that virtually every fertile women observes, or can be trained to observe, the secretion of a particular pattern of mucus coming from the cervix around the time of fertility; this appears at the vulva as a vaginal discharge. The temperature-rhythm combination continued to be used while careful observations were made to determine those days in the cycle when it is possible for the woman to become pregnant, when she is unable to do so, and the day on which she was most likely to become pregnant. It was only after the self-observation of the mucus pattern and the application of guidelines appropriate to the desire of the couple to achieve or to avoid pregnancy in the cycle that the temperature-rhythm calculations were abandoned. By 1962 a decision was made to publish a book regarding these studies and the conclusions that had been reached.

It was in this same year, 1962, that Dr James Brown took up an appointment at the Royal Women's Hospital, Melbourne. The international reputation that he had acquired in Edinburgh, Scotland, particularly in the development of a method for measuring oestrogen and progesterone metabolites in urine, had preceded him. Soon afterwards he was approached and given information about our Melbourne work and was asked if he would submit all of our conclusions to the evaluation of his laboratory techniques. He immediately agreed to this request and over the 38 years which have elapsed since this first meeting, we have had the good fortune to have had his active collaboration and guidance. He had immediately undertaken the daily measurements of oestrogen and progesterone metabolites in the urine of two women which confirmed our judgments, and this information was added to the content of the book, which was published in 1964. We decided to call this new method The Ovulation Method in order to emphasize that attention was now taken away from menstruation and directed to ovulation, which is the more important event in the women's cycle.

It had been observed that the characteristics of the mucus secretion, determined by the sensation produced by its presence on the vulva and by any visual observations that might be made, is a changing pattern. This could now be related to the hormonal patterns, beginning with the progressive rise of oestrogens up to a peak about a day before what was now described as the Peak day, the day on which there was the best possible chance of a woman becoming pregnant. This was quickly followed by a change in the physical characteristics of the mucus which was now reflecting the rise of progesterone just before ovulation. In the pre-ovulatory phase the days before the development of the mucus symptom were recognized as infertile and after the fertile phase it was established that the rest of the cycle was also infertile after allowing a count of 3 days past the mucus symptom. These conclusions were reached after a careful study over some years, undertaken by couples who were now anxious to achieve pregnancy, in which a single act of intercourse was placed within the days of possible fertility in successive cycles, working backwards from the fourth day after the Peak symptom.

The precise time of ovulation was now able to be determined by daily measurements of oestrogen and progesterone metabolites. It was clear that ovulation occurs on the day of the Peak symptom or the following day, rarely on the second day after the Peak so that allowing for the possibility of ovum survival for 24 hours, a count of 3 days after the Peak symptom had to be applied to be sure that by the beginning of the fourth day after the Peak every woman had ovulated and the egg had disintegrated. So the earlier allowance made for the avoidance of intercourse on 3 days following the end of the mucus pattern was now more precisely translated to a count of 3 days to allow for the disintegration of the ovum following the Peak of the mucus symptom.

Soon after Dr Brown's collaboration began, Dr Evelyn Billings also joined in the research. At the beginning the work had been in the hands of Dr John Billings, working with the help of an experienced marriage consultant, Rev. Maurice Catarinich. Dr Evelyn Billings undertook a survey of pre-menopausal women, leading to the recognition of infertility even in the presence of a discharge other than mucus. A variety of discharges exist, and she was able, with invaluable help from Dr Brown, to demonstrate that if the discharges, whenever they were observed over a period of two weeks remained unchanged and no bleeding had occurred, they were an indication of infertility. The discharges indicating infertility now supplemented the infertile days of dryness, the "dry days" when there is no discharge at all.

It was soon after this time that Dr Brown was awarded a personal professorial appointment within the University of Melbourne, as a special honour for his brilliant laboratory work as Director of the Research Laboratory at the Royal Women's Hospital. He was now involved in the development of what he called an Ovarian Monitor, a device which can quickly and accurately measure the metabolites of oestrone and pregnanediol in a timed specimen of urine, giving values which reflect accurately the levels of circulating oestrogen and progesterone. The Monitor is able to be used in the laboratory or even by a woman in her own home, It has been of immense value in assisting apparently infertile couples to achieve pregnancy, and is also very useful in confirming all the basic principles and guidelines of the Billings Ovulation Method and for investigating the causes of unexplained bleeding from the uterus and other gynaecological disorders.

It was in the 1970s that we learned about the excellent research of Professor Erik Odeblad of the Department of Medical Biophysics, University of UmeˆÉ¬ÉˆÇ¬´, Sweden. He had been studying the physical properties of the various cervical secretions and was beginning to define different types of mucus, with appropriate functions. He too has collaborated with Professor Brown and ourselves for more than 20 years up to the present time. It had gradually become clear that sperm survival and sperm transport within the woman's reproductive system are critically dependent upon the presence of a healthy mucus pattern.

An important feature of these disciplines within medical research--the clinical studies of the cervical mucus symptom, of the ovarian hormonal pattern and of the physical characteristics of the various types of cervical mucus--have displayed a remarkable congruence. There is no contradiction between any of the results of these individual and collaborative projects. It is common practice now for the phases of the cycle and the occurrence of ovulation to be determined by ultrasound studies, but it is easier and more accurate to do this by the Billings Ovulation Method, as it is now being named, following the recommendation of a Committee of the World Health Organization.

The woman who knows the Billings Ovulation Method will always know the day on which she has conceived and this will provide for a reliable estimation of the expected date of delivery. It therefore protects the woman from imprudent interference with the pregnancy when the calculation has been made from the date of the last menstrual period.

It must also be pointed out that the study of natural family planning offers special research possibilities because the gynaecological health of the woman has not been disturbed nor has her fertility been suppressed by any medication, however administered, nor by any instrument or surgical operation. There is therefore the opportunity to study any change from normal: infertility, irregular bleeding, disorders produced by ovarian cysts or tumours, vaginal infections and so on.

Professor Brown's work has encompassed many areas of interest to medical science beyond his great service to natural family planning. He developed impressively sound explanations of the interaction between the pituitary and the ovarian hormones in both the normal fertile cycle and those incidences of physiological and pathological alterations from it. He made very interesting observations of FSH and oestrogen levels at menopause and afterwards. He explained the action of prolactin in delaying the return of fertility for a variable time following child birth and the establishment of breast-feeding. He made interesting observations of the progressive suppression of fertility in women undertaking strenuous physical exertion over a long period of time, for example those involved in running marathons and the long training required for such athletic pursuits. His studies of infertility influenced his opinions regarding the polycystic ovary syndrome. He had an interest in the oestrogen levels in women developing breast cancer and suspected the accumulation of carcinogenic material within the mammary ducts as a cause of the cancer, pointing out that this risk is removed by pregnancy and lactation. He was one of the first to recognize that certain adreno-genital disorders can cause a raised level of progesterone in the circulation, and through his assistance to those undertaking studies of prolactin levels and infertility knew that a raised prolactin level can result from pituitary tumours and the ingestion of certain drugs.

This monograph has been written to help women understand why the rules of the Billings Ovulation Method are as they are and to give women confidence that they are in control of their fertility at all times. However, this monograph is more than that. It should come to be regarded as a classic in medical literature. It is an example of Professor Brown's unique contribution to the protection and restoration of women's health, with particular reference to her ability to conceive and nurture children. His superb scientific work has been of inestimable value not only to the disciplines of obstetrics and gynaecology, but especially to the dignity and self esteem of women all over the world.

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