Editing Calendar-based contraceptive methods (section)

===Later 20th century to present===
In the first half of the 20th century, most users of the rhythm method were Catholic; they were following their church's teaching that all other methods of birth control were sinful.  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."  This is interpreted as favoring the then-new, more reliable symptoms-based [[fertility awareness]] methods over the rhythm method.  Currently, many fertility awareness teachers consider the rhythm method to have been obsolete for at least 20 years.<ref name="tcoyf" />

New attention was drawn to calendar-based methods in 2002, when the Institute for Reproductive Health at [[Georgetown University]] introduced the Standard Days Method.  Designed to be simpler to teach and use than the older rhythm method, the Standard Days Method was initially integrated piloted in 30 [[family planning]] programs worldwide. However, only 16 countries scaled up beyond pilots, with limited adoption since.<ref>{{cite journal |last1=Weis |first1=Julianne |last2=Festin |first2=Mario |title=Implementation and Scale-Up of the Standard Days Method of Family Planning: A Landscape Analysis |journal=Global Health, Science and Practice |pages=114–124 |doi=10.9745/GHSP-D-19-00287 |date=30 March 2020|volume=8 |issue=1 |pmid=32033980 |pmc=7108942 }}</ref><ref>{{cite journal |last1=Marston |first1=Cicely A. |last2=Church |first2=Kathryn |title=Does the evidence support global promotion of the calendar-based Standard Days Method® of contraception? |url=https://pubmed.ncbi.nlm.nih.gov/26794286/ |journal=Contraception |access-date=15 October 2024 |pages=492–497 |doi=10.1016/j.contraception.2016.01.006 |date=June 2016|volume=93 |issue=6 |pmid=26794286 }}</ref><ref>{{cite journal |last1=Wright |first1=Kelsey |last2=Iqteit |first2=Hiba |last3=Hardee |first3=Karen |title=Standard Days Method of contraception: Evidence on use, implementation, and scale up |url=https://knowledgecommons.popcouncil.org/departments_sbsr-rh/885/ |website=Reproductive Health |access-date=15 October 2024 |doi=10.31899/rh9.1057 |date=1 January 2015}}</ref>