Terminology
Some sources may treat the terms rhythm method and fertility awareness as synonymous. However, fertility awareness is usually used as a broad term that includes tracking basal body temperature and cervical mucus as well as cycle length. The World Health Organization considers the rhythm method to be a specific type of calendar-based method, and calendar-based methods to be only one form of fertility awareness.
More effective than calendar-based methods, systems of fertility awareness that track basal body temperature, cervical mucus, or both, are known as symptoms-based methods. Teachers of symptoms-based methods take care to distance their systems from the poor reputation of the rhythm method. Many consider the rhythm method to have been obsolete for at least 20 years, and some even exclude calendar-based methods from their definition of fertility awareness.
Some sources may treat the terms rhythm method and natural family planning as synonymous. In the early 20th century, the calendar-based method known as the rhythm method was promoted by members of the Roman Catholic Church as the only morally acceptable form of family planning. Methods accepted by this church are referred to as natural family planning (NFP): so at one time, the term "the rhythm method" was synonymous with NFP. Today, NFP is an umbrella term that includes symptoms-based fertility awareness methods and the lactational amenorrhea method as well as calendar-based methods such as rhythm. This overlap between uses of the terms "the rhythm method" and "natural family planning" may contribute to confusion.
The term "the rhythm method" is sometimes used, in error, to describe the behavior of any people who have unprotected vaginal intercourse, yet wish to avoid pregnancy.
Read more about this topic: Calendar-based Contraceptive Methods