Natural fertility regulation (NFR) methods could provide family planning (avoiding or achieving pregnancy) naturally through conforming to the women’s reproductive cycle without the use of drugs or devices. NFR originated about 60 years ago from the rhythmic method, but this method was not scientifically based. Its deadly shortcoming is the prediction of the coming events on the basis of the past rhythm is therefore destined to be inaccurate with a failure rate of more than 20%. A milestone in the NFR study is the discovery of the intrinsic relationship between the cervical mucus, the hormonal balance and the fertility status of women by the Billings group. It was shown that the changes in the cervical mucus correlated with the sex hormone levels in the women, thus the fertile status could be determined by observing the characteristics of the cervical mucus at the vulva. In this way the Billings Ovulation Method (BOM) overcomes the fatal weakness of early natural family planning methods in predicting the current events on the basis of past happening, and lays the foundation of scientific NFR research.
In the 30 years fertile life of women, only a few days in each cycle are fertile and the rest of the time is infertile. People of insight have long considered making use of this natural phenomenon to regulate fertility. Early methods of natural family planning (rhythm, basal body temperature, symptothermal, etc.) are unsatisfactory for fertility regulation and the Chinese people did not accept them. In the early 60’s, Drs. J.J. and E.L. Billings and their colleagues discovered the interrelationship between the cervical mucus and the cyclic changes in the ovarian hormones and fertility and alleged the use of mucus symptom as the main index of ovulation and fertility applicable to all phases of female reproductive life. This is a milestone in the study of natural family planning.