Editing Calendar-based contraceptive methods (section)

==Types and effectiveness==
Most menstrual cycles have several days at the beginning that are infertile (pre-ovulatory infertility), a period of fertility, and then several days just before the next menstruation that are infertile (post-ovulatory infertility). The first day of red bleeding is considered day one of the menstrual cycle. To use these methods, a woman is required to know the length of her menstrual cycles.

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. The typical-use failure rate of calendar-based methods is 25% per year.<ref name="hatcher">{{cite book | first=RA | last=Hatcher | author2=Trussel J | author3=Stewart F | year=2000 | title=Contraceptive Technology | edition=18th | publisher=Ardent Media | location=New York | isbn=0-9664902-6-6 | url=http://www.contraceptivetechnology.com/table.html | display-authors=etal | access-date=2006-10-02 | archive-url=https://web.archive.org/web/20080531095926/http://www.contraceptivetechnology.com/table.html | archive-date=2008-05-31 | url-status=dead }}</ref>

===Rhythm method (Knaus–Ogino method)===
To find the estimated length of the pre-ovulatory infertile phase, eighteen (18) is subtracted from the length of the woman's shortest cycle. To find the estimated start of the post-ovulatory infertile phase, eleven (11) is subtracted from the length of the woman's longest cycle.<ref name="kippleycalendar" /> A woman whose menstrual cycles ranged in length from 30 to 36 days would be estimated to be infertile for the first 11 days of her cycle (30-19=11), to be fertile on days 12–25, and to resume infertility on day 26 (36-10=26). When used to avoid pregnancy, such fertility awareness-based methods have a typical-use failure rate of 25% per year.<ref name="hatcher"/>

===Standard days method===
[[File:Geburtenkontrollkette.jpg|thumb|alt=a birth control chain calendar necklace|A [[CycleBeads]] birth control chain, used for a rough estimate of fertility based on days since menstruation]]

Developed at [[Georgetown University]]'s Institute for Reproductive Health, the standard days method is a variation of the rhythm method that has a simpler rule set and is more effective than the Knaus–Ogino method.<ref name="hatcher"/><ref name="Arévalo M, Jennings V, Sinai I 2002 333–8">{{cite journal |vauthors=Arévalo M, Jennings V, Sinai I |title=Efficacy of a new method of family planning: the Standard Days Method. | journal = Contraception | volume = 65 | issue = 5 |pages=333–8 |year=2002 | pmid = 12057784 | url=https://irh.org/wp-content/uploads/2013/04/Efficacy_SDM_2002.pdf | doi = 10.1016/S0010-7824(02)00288-3}}</ref> 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. The standard days method is only effective for women whose cycles are consistently between 26 and 32 days in length; it is estimated that between 50% and 60% of women of reproductive age satisfy this condition.<ref name="WF"/> In this system:
* Days 1–7 of a woman's menstrual cycle are considered infertile
* Days 8–19 are considered fertile; considered unsafe for unprotected intercourse
* Day 20 through the end of the cycle are considered infertile.

When used to avoid pregnancy, the standard days method has been estimated<ref>[https://irh.org/wp-content/uploads/2013/04/SDM_Top_20_FAQs_English.pdf «Standard Days Method® and CycleBeads®: Top 20 Most Frequently Asked Questions»]. ''Institute for Reproductive Health''.</ref> to have perfect-use efficacy of 95% and typical-use efficacy of 88%.<ref name="Arévalo M, Jennings V, Sinai I 2002 333–8"/><ref name="WF">Weis, Julianne; Festin, Mario (2020-02-07). [https://www.ghspjournal.org/content/8/1/114 «Implementation and Scale-Up of the Standard Days Method of Family Planning: A Landscape Analysis»]. ''Global Health: Science and Practice'' '''8''' (1): 114-124. {{ISSN|2169-575X}}. {{doi|10.9745/ghsp-d-19-00287}}.</ref> These figures are based on a 2002 study in Bolivia, Peru, and the Philippines of women of reproductive age having menstrual cycles between 26 and 32 days,<ref name="Arévalo M, Jennings V, Sinai I 2002 333–8"/><ref>{{cite book|title=Management of Common Problems in Obstetrics and Gynecology, 5th ed.|editor-last=Goodwin|editor-first=T. Murphy|editor2-last=Montoro|editor2-first=Martin N.|editor3-last=Muderspach|editor3-first=Laila|editor4-last=Paulson|editor4-first=Richard|editor5-last=Roy|editor5-first=Subir|publisher=Wiley-Blackwell|year=2010|asin=B005D7EP92}}</ref>{{rp|505}} and on a 2014 study in Turkey.<ref>Kursun, Zerrin; Cali, Sanda; Sakarya, Sibel (2014-06). [https://pubmed.ncbi.nlm.nih.gov/24597662/ «The Standard Days Method(®): efficacy, satisfaction and demand at regular family planning service delivery settings in Turkey»]. ''The European Journal of Contraception & Reproductive Health Care: The Official Journal of the European Society of Contraception'' '''19''' (3): 203-210. {{ISSN|1473-0782}}. {{PMID|24597662}}. {{doi|10.3109/13625187.2014.890181}}.</ref> However, other researchers have criticized the methodology of the first study, have stated that the 95% figure has been presented to the public in misleading ways, and have argued that the true efficacy figures are likely to be much lower.<ref>{{Cite journal|last1=Marston|first1=Cicely A.|last2=Church|first2=Kathryn|date=2016-06-01|title=Does the evidence support global promotion of the calendar-based Standard Days Method® of contraception?|url=http://www.contraceptionjournal.org/article/S0010-7824(16)00005-6/fulltext|journal=Contraception|language=en|volume=93|issue=6|pages=492–497|doi=10.1016/j.contraception.2016.01.006|pmid=26794286|issn=0010-7824|doi-access=free}}</ref> Another meta study indicated that typical-use efficacy ranged between 90% and 82%, a bit lower than the 88% figure originally found.<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>