The Natural Cycles application is a fertility awareness-based contraceptive method that uses dates of menstruation and basal body temperature to inform couples whether protected intercourse is needed to prevent pregnancies. Our purpose with this study is to investigate the contraceptive efficacy of the mobile application by evaluating the perfect- and typical-use Pearl Index.
In this prospective observational study, 22,785 users of the application logged a total of 18,548 woman-years of data into the application. We used these data to calculate typical- and perfect-use Pearl Indexes, as well as 13-cycle pregnancy rates using life-table analysis.
We found a typical-use Pearl Index of 6.9 pregnancies per 100 woman-years [95% confidence interval (CI): 6.5–7.2], corrected to 6.8 (95% CI: 6.4–7.2) when truncating users after 12 months. We estimated a 13-cycle typical-use failure rate of 8.3% (95% CI: 7.8–8.9). We found that the perfect-use Pearl Index was 1.0 pregnancy per 100 woman-years (95% CI: 0.5–1.5). Finally, we estimated that the rate of pregnancies from cycles where the application erroneously flagged a fertile day as infertile was 0.5 (95% CI: 0.4–0.7) per 100 woman-years. We estimated a discontinuation rate over 12 months of 54%.
This study shows that the efficacy of a contraceptive mobile application is higher than usually reported for traditional fertility awareness-based methods. The application may contribute to reducing the unmet need for contraception.
The measured typical and perfect-use efficacies of the mobile application Natural Cycles are important parameters for women considering their contraceptive options as well as for the clinicians advising them. The large available data set in this paper allows for future studies on acceptability, for example, by studying the efficacy for different cohorts and geographic regions.
Fertility awareness, Mobile application, Contraceptive efficacy, Pearl Index
The aim of the study was to evaluate the effectiveness of a fertility awareness-based method supported by a mobile-based application to prevent unwanted pregnancies as a method of natural birth control.
In a retrospective analysis, the application’s efficiency as a contraceptive method was examined on data from 4054 women who used the application as contraception for a total of 2085 woman-years.
The number of identified unplanned pregnancies was 143 during 2053 woman-years, giving a Pearl Index of 7.0 for typical use. Ten of the pregnancies were due to the application falsely attributing a safe day within the fertile window, producing a perfect-use Pearl Index of 0.5. Calculating the cumulative pregnancy probability by life-table analysis resulted in a pregnancy rate of 7.5% per year (95% confidence interval 5.9%, 9.1% per year).
The application appears to improve the effectiveness of fertility awareness-based methods and can be used to prevent pregnancies if couples consistently protect themselves on fertile days.
The aim of the study was to evaluate the ability of a novel web and mobile application to identify a woman’s ovulation day and fertile window, in order to use it as a method of natural birth control.
A retrospective study was performed on 1501 cycles of 317 women aged 18 to 39 years. Women entered their basal body temperatures, ovulation test results and date of menstruation into the application.
The mean delay from the first positive ovulation test to the temperature-based estimation of the ovulation day was 1.9 days; the length of the luteal phase varied on average by 1.25 days per user. Only 0.05% of non-fertile days were falsely attributed and found within the fertile window.
The method is effective at identifying a user’s ovulation day and fertile window and can, therefore, be used as a natural method of birth control.
Basal body temperature; Fertile window; Fertility awareness; Fertility monitor; Natural birth control; Natural family planning