Calendar-based contraceptive methods

This system was a main form of birth control available to Catholic couples for several decades, until the popularization of symptoms-based fertility awareness methods.

[1] However, fertility awareness is usually used as a broad term that includes tracking basal body temperature and cervical mucus as well as cycle length.

Similarly, a Chinese sex manual written close to the year 600 stated that only the first five days following menstruation were fertile.

[9] Scientific advances prompted a number of secular thinkers to advocate periodic abstinence to avoid pregnancy:[11] in the 1840s it was discovered that many animals ovulate during estrus.

[9][10] In 1854, an English physician named George Drysdale correctly taught his patients that the days near menstruation are the least fertile, but this remained the minority view for the remainder of the 19th century.

[9] In 1905 Theodoor Hendrik van de Velde, a Dutch gynecologist, showed that women only ovulate once per menstrual cycle.

[12] In the 1920s, Kyusaku Ogino, a Japanese gynecologist, and Hermann Knaus, from Austria, working independently, each made the discovery that ovulation occurs about fourteen days before the next menstrual period.

In 1930, Johannes Smulders, a Roman Catholic physician from the Netherlands, used Knaus and Ogino's discoveries to create a method for avoiding pregnancy.

Smulders published his work with the Dutch Roman Catholic medical association, and this was the official rhythm method promoted over the next several decades.

[13] In 1932 a Catholic physician, Dr. Leo J Latz, published a book titled The Rhythm of Sterility and Fertility in Women describing the method,[11] and the 1930s also saw the first U.S.

In 1968 the encyclical Humanae vitae included the statement, "It is supremely desirable... that medical science should by the study of natural rhythms succeed in determining a sufficiently secure basis for the chaste limitation of offspring."

Imperfect use of calendar-based methods would consist of not correctly tracking the length of the woman's cycles, thus using the wrong numbers in the formula, or of having unprotected intercourse on an identified fertile day.

The discipline required to keep accurate records of menstrual cycles, and to abstain from unprotected intercourse, makes imperfect use fairly common.

To find the estimated start of the post-ovulatory infertile phase, eleven (11) is subtracted from the length of the woman's longest cycle.

[18][20] A product called CycleBeads was developed alongside the method to help the user keep track of estimated high and low fertility points during her menstrual cycle.

Of commonly known methods of birth control, only the cervical cap and contraceptive sponge have comparably high failure rates.

[19] It has been suggested that pregnancies resulting from failures of periodic abstinence methods are at increased risk of miscarriage and birth defects due to aged gametes at the time of conception.