{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,20]],"date-time":"2026-05-20T03:15:15Z","timestamp":1779246915392,"version":"3.51.4"},"reference-count":9,"publisher":"BMJ","issue":"3","funder":[{"DOI":"10.13039\/100009633","name":"Eunice Kennedy Shriver National Institute of Child Health and Human Development","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100009633","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Open"],"accepted":{"date-parts":[[2019,2,13]]},"published-print":{"date-parts":[[2019,3]]},"abstract":"<jats:sec>\n                    <jats:title>Objective<\/jats:title>\n                    <jats:p>To investigate the association between contraceptive effectiveness of Natural Cycles and users\u2019 previous choice of contraceptive, and to evaluate the impact of shifting from other methods to Natural Cycles on the risk of unintended pregnancy.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Setting<\/jats:title>\n                    <jats:p>Natural Cycles mobile application.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Participants<\/jats:title>\n                    <jats:p>16 331 Natural Cycles users in Sweden for the prevention of pregnancy.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Outcome measures<\/jats:title>\n                    <jats:p>Risk of unintended pregnancy.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Study design<\/jats:title>\n                    <jats:p>Real world evidence was collected from Natural Cycles users regarding contraceptive use prior to using Natural Cycles and sexual activity while using Natural Cycles. We calculated the typical use 1-year Pearl Index (PI) and 13-cycle failure rate of Natural Cycles for each cohort. The PI was compared with the population PI of their stated previous methods.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>For women who had used condoms before, the PI of Natural Cycles was the lowest at 3.5\u00b10.5. For women who had used the pill before, the PI of Natural Cycles was the highest at 8.1\u00b10.6. The frequency of unprotected sex on fertile days partially explained some of the observed variation in PI between cohorts. 89% of users switched to Natural Cycles from methods with higher or similar reported PIs.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>The effectiveness of Natural Cycles is influenced by previous contraceptive choice and this should be considered when evaluating the suitability of the method for the individual. We estimate that Natural Cycles usage can reduce the overall likelihood of having an unintended pregnancy by shifting usage from less effective methods.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmjopen-2018-026474","type":"journal-article","created":{"date-parts":[[2019,3,23]],"date-time":"2019-03-23T12:45:25Z","timestamp":1553345125000},"page":"e026474","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":22,"title":["Typical use effectiveness of Natural Cycles: postmarket surveillance study investigating the impact of previous contraceptive choice on the risk of unintended pregnancy"],"prefix":"10.1136","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9992-3769","authenticated-orcid":false,"given":"Jonathan","family":"Bull","sequence":"first","affiliation":[{"name":"Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Simon","family":"Rowland","sequence":"additional","affiliation":[{"name":"Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Olof","family":"Lundberg","sequence":"additional","affiliation":[{"name":"Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Elina","family":"Berglund-Scherwitzl","sequence":"additional","affiliation":[{"name":"Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kristina","family":"Gemzell-Danielsson","sequence":"additional","affiliation":[{"name":"Department of Women\u2019s and Children\u2019s Health, Karolinska Universitetssjukhuset, Stockholm, Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"James","family":"Trussell","sequence":"additional","affiliation":[{"name":"Office of Population Research, Princeton University, Princeton, New Jersey, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Raoul","family":"Scherwitzl","sequence":"additional","affiliation":[{"name":"Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"239","published-online":{"date-parts":[[2019,3,23]]},"reference":[{"key":"2025120618071463000_9.3.e026474.1","doi-asserted-by":"crossref","first-page":"97","DOI":"10.1023\/A:1006534632583","article-title":"Retrospective clinical trial of contraceptive effectiveness of the electronic fertility indicator Ladycomp\/Babycomp","volume":"14","author":"Freundl","year":"1998","journal-title":"Adv Contracept"},{"key":"2025120618071463000_9.3.e026474.2","doi-asserted-by":"crossref","first-page":"e5","DOI":"10.2196\/resprot.6886","article-title":"Assessing the efficacy of an app-based method of family planning: The dot study protocol","volume":"6","author":"Simmons","year":"2017","journal-title":"JMIR Res Protoc"},{"key":"2025120618071463000_9.3.e026474.3","doi-asserted-by":"crossref","first-page":"37","DOI":"10.1186\/s12978-018-0479-6","article-title":"Improving usability and pregnancy rates of a fertility monitor by an additional mobile application: results of a retrospective efficacy study of Daysy and DaysyView app","volume":"15","author":"Koch","year":"2018","journal-title":"Reprod Health"},{"key":"2025120618071463000_9.3.e026474.4","doi-asserted-by":"publisher","DOI":"10.3109\/13625187.2014.988210"},{"key":"2025120618071463000_9.3.e026474.5","doi-asserted-by":"crossref","first-page":"234","DOI":"10.3109\/13625187.2016.1154143","article-title":"Fertility awareness-based mobile application for contraception","volume":"21","author":"Berglund Scherwitzl","year":"2016","journal-title":"Eur J Contracept Reprod Health Care"},{"key":"2025120618071463000_9.3.e026474.6","doi-asserted-by":"crossref","first-page":"420","DOI":"10.1016\/j.contraception.2017.08.014","article-title":"Perfect-use and typical-use Pearl Index of a contraceptive mobile app","volume":"96","author":"Berglund Scherwitzl","year":"2017","journal-title":"Contraception"},{"key":"2025120618071463000_9.3.e026474.7","unstructured":"WHO. Fact sheet on family planning \/ contraception. 2016 http:\/\/www.who.int\/mediacentre\/factsheets\/fs351\/en\/."},{"key":"2025120618071463000_9.3.e026474.8","doi-asserted-by":"publisher","DOI":"10.1016\/j.contraception.2011.01.021"},{"key":"2025120618071463000_9.3.e026474.9","unstructured":"Kalbfleisch JD , Prentice RL . The statistical analysis of failure time data. New York: Wiley, 2011. https:\/\/books.google.se\/books?id=BR4Kq-a1MIMC."}],"updated-by":[{"DOI":"10.1136\/bmjopen-2018-026474corr1","type":"correction","label":"Correction","source":"publisher","updated":{"date-parts":[[2019,6,14]],"date-time":"2019-06-14T00:00:00Z","timestamp":1560470400000}}],"container-title":["BMJ Open"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.1136\/bmjopen-2018-026474","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,12,7]],"date-time":"2025-12-07T02:07:23Z","timestamp":1765073243000},"score":1,"resource":{"primary":{"URL":"https:\/\/bmjopen.bmj.com\/lookup\/doi\/10.1136\/bmjopen-2018-026474"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,3]]},"references-count":9,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2019,3,23]]},"published-print":{"date-parts":[[2019,3]]}},"alternative-id":["10.1136\/bmjopen-2018-026474"],"URL":"https:\/\/doi.org\/10.1136\/bmjopen-2018-026474","relation":{},"ISSN":["2044-6055","2044-6055"],"issn-type":[{"value":"2044-6055","type":"print"},{"value":"2044-6055","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,3]]}}}