Once, the only natural family planning method available was the Rhythm Method. This Method is based on the finding that ovulation occurs, on a single day, eleven to sixteen days before menstrual bleeding starts. This gives a woman with near regular cycles a means of calculating the days when she is most likely fertile. However no woman is always regular. Inevitably there are significant variations in cycle length – caused by emotional stress, after pregnancy, or close to the menopause.

Clearly what was needed was a marker of fertility that women themselves could recognise. With this in mind, Dr John Billings made a search of the medical literature in 1953. He found several accounts of stringy lubricative mucus, produced at about the time of ovulation by the cells lining the cervix.

Could the mucus be used as a signal of fertility? After questioning a small number of women, it became clear that the occurrence of different types of discharge during the menstrual cycle was a familiar observation. It then became a matter of determining whether a typical pattern existed during the cycle, and whether women could identify their fertile phase.

With the co-operation of hundreds of women, a standard mucus pattern quickly emerged. It became evident that the sensation produced by the mucus, as well as its appearance, could enable all women to recognise the onset of fertility. Even blindness proved to be no barrier to learning. And the pattern appeared similar for women in different societies.

By the mid-1960s a prolonged clinical study of the women's charts had been completed, and a set of guidelines formulated for fertility control.  At this stage, only the mucus pattern associated with ovulation, and the infertile phase following it, had been identified.  Initially Rhythm calculations were used to determine the early part of the cycle and basal body temperatures were taken to verify ovulation.

The involvement of Dr Evelyn Billings in research began in 1966, with the recognition of the infertile patterns of either dryness or discharge before ovulation.  This was at the same time a fascinating discovery and a tremendous relief because couples no longer had to endure periods of prolonged abstinence.  As long as the discharge or dryness that a woman correctly identified as her infertile pattern remained unchanged, intercourse could not result in conception.

When Dr Evelyn Billings began teaching the Method it quickly became obvious that woman-to-woman teaching was the most effective way of getting the message across.

Each step along the way to establishing reliable and universally applicable guidelines for fertility control was tested many times and correlated with hormonal studies. The unchanging pattern before ovulation corresponded with a basic low hormonal level and was thus called the Basic Infertile Pattern.

In 1971 temperature measurements and Rhythm calculations were discontinued and it was when the World Health Organisation undertook the 5-nation trial that they recommended that this Method be called the Billings Ovulation Method™ to identify it from other methods. Now refined and validated in many studies, it stands alone for all circumstances of reproductive life.