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Typical use effectiveness of Natural Cycles: postmarket surveillance study investigating the impact of previous contraceptive choice on the risk of unintended pregnancy
  1. Jonathan Bull1,
  2. Simon Rowland1,
  3. Olof Lundberg1,
  4. Elina Berglund-Scherwitzl1,
  5. Kristina Gemzell-Danielsson2,
  6. James Trussell3,
  7. Raoul Scherwitzl1
  1. 1 Department of Medical Communications, Natural Cycles Nordic AB, Stockholm, Sweden
  2. 2 Department of Women’s and Children’s Health, Karolinska Universitetssjukhuset, Stockholm, Sweden
  3. 3 Office of Population Research, Princeton University, Princeton, New Jersey, USA
  1. Correspondence to Dr Raoul Scherwitzl; raoul.scherwitzl{at}


Objective To investigate the association between contraceptive effectiveness of Natural Cycles and users’ previous choice of contraceptive, and to evaluate the impact of shifting from other methods to Natural Cycles on the risk of unintended pregnancy.

Setting Natural Cycles mobile application.

Participants 16 331 Natural Cycles users in Sweden for the prevention of pregnancy.

Outcome measures Risk of unintended pregnancy.

Study design 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.

Results For women who had used condoms before, the PI of Natural Cycles was the lowest at 3.5±0.5. For women who had used the pill before, the PI of Natural Cycles was the highest at 8.1±0.6. 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.

Conclusion 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.

  • contraception
  • fertility app
  • family planning
  • fertility awareness
  • information technology
  • telemedicine

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  • Contributors JB contributed to the study design, data analysis and interpretation, and manuscript preparation. SR and OL contributed to the study design, data interpretation and manuscript preparation. EB-S and RS contributed to the study design, data acquisition and final approval. KG-D and JT contributed to the study design, data interpretation and final approval.

  • Funding The study was funded by Natural Cycles Nordic AB. JT acknowledges the support from an infrastructure grant for population research from the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health, P2C HD047879.

  • Competing interests EB-S and RS are the scientists behind the application Natural Cycles and the founders of the company with stock ownership. JB, OL and SR are employed by Natural Cycles Nordic AB. KG-D serves on the medical advisory board of Natural Cycles and has received honorarium for participating in advisory boards and/or giving presentations for matters related to contraception and fertility regulation for Ferring, Exelgyn and Mithra. JT declares explicitly that there are no conflicts of interest in connection with this article.

  • Ethics approval The study protocol wasreviewed and approved by the regional ethic s committee (EPN,Stockholm, diary number 2017/563-31).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement There is no additional unpublished data from this study.

  • Patient consent for publication Not required.

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