FemTech Series

Natural Cycles App Effectiveness to Prevent Pregnancy: A Review of Research

By: Madison Hoover

Director’s Note: Our FemTech Series continues with a summary of research exploring the effectiveness of the Natural Cycles application (app). Summarized by Madison Hoover, a former FACTS elective participant, this 2021 study was published in The Journal of Women’s Health. [1] As more women turn to fertility awareness-based methods (FABMs), an increasing number of fertility tracking apps have entered the market. Drawing from a prospective cohort of users of the Natural Cycles app in the United States, Pearson et al analyzed the application’s effectiveness to prevent pregnancy.

Introduction

Fertility awareness-based methods (FABMs) address the growing need for safe and effective forms of family planning that are non-invasive and non-hormonal. With FABMs, woman learn to track physiologic biomarkers (eg, cervical mucus, basal body temperature, urinary hormones) to identify their potential fertile window. A couple may avoid or choose to have intercourse based on the desire to achieve or avoid pregnancy.

Although hundreds of fertility tracking apps are now available to help women monitor their menstrual cycle and fertile window, many rely on a calendar method or algorithm without effectiveness data. Natural Cycles, the first FDA-cleared app for birth control available in the United States, utilizes one or more of the physiologic biomarkers essential to FABMs. The app works by tracking the user’s menstrual cycle and basal body temperature (BBT) with an option to include urinary luteinizing hormone (LH) to identify fertile days. Fertile days are marked in red and non-fertile days in green. On fertile days, the app will notify the user to either abstain from sex or use a barrier method. The app allows couples to input whether they use a barrier method or abstain from sexual intercourse.

“Natural Cycles, the first FDA-cleared app for birth control available in the United States … works by tracking the user’s menstrual cycle and basal body temperature with an option to include urinary luteinizing hormone to identify fertile days.”

The goal of the study by Pearson et al [1] was to assess the effectiveness of the Natural Cycles app at preventing pregnancy. It also aimed to identify the key demographics of current users of the app in the US cohort. The researchers also sought to compare their US results with previous studies in a more general demographic that revealed an 8.3% failure rate with typical use.

Methodology

This prospective cohort study included 5,879 women who contributed an average of 10.5 months of data. Women were chosen from Natural Cycles app users who enrolled for an annual subscription between September 2017 and March 2018 and were using the app as their primary means of contraception. The participants were 18 to 45 years of age. Upon registration, demographic and historical information was obtained through an intake questionnaire. There were no instructions or rules for participation beyond meeting the criteria listed above, and data collection was strictly through user entry into the app.

Results

The results were calculated using the Pearl index, which represents the number of pregnancies per 100 women per year. The typical use Pearl index for the Natural Cycles app was 6.2; this means that with typical use, 6.2 pregnancies occurred for every 100 women. Perfect use involved measuring and recording BBT more than 70% of days and using abstinence or barrier methods on days marked as fertile. The perfect use Pearl index was 2.0. The 13-cycle cumulative pregnancy probability was found to be 8.1%, which is comparable to the 8.3% found in previous studies.

Women aged 29 to 34 had a significantly higher pregnancy probability of 8.8% compared to users aged 35 to 45 years, whose pregnancy probability was 5%. On fertile days, participants used different behaviors or methods to prevent pregnancy: 52.8% reported using condoms, 10.9% relied on abstinence, and 25.2% reported use of withdrawal.

“On fertile days, participants used different behaviors or methods to prevent pregnancy: 52.8% reported using condoms, 10.9% relied on abstinence, and 25.2% reported use of withdrawal.”

Demographics for the US cohort revealed an average age of 30 with an average body mass index (BMI) of 24. Also, 86.1% of users reported being in a stable relationship, and 84.3% indicated having a university degree level of education or higher. The researchers collected data on previous contraceptive use. Interestingly, former users of hormonal birth control had a higher 13-cycle cumulative pregnancy probability of 7.5% compared to 4.7% for women who had never used hormonal birth control.

Discussion

Several aspects of this study are limited by relying on self-reporting. For example, users were often inconsistent in logging BBT, and many did not record all intercourse or denote whether they used barrier methods or abstained from sexual relations. Participants received few instructions, and despite noting a desire to prevent pregnancy, there is likely a need to classify the strength of commitment to this goal. The data reinforce this notion, and reveal that 57% of intercourse was logged on fertile days, with 43% reported on non-fertile days. Yet, this could also be explained by a desire to track “higher risk” intercourse accurately, and would warrant further investigation.

“Despite noting a desire to prevent pregnancy, there is likely a need to classify the strength of commitment to this goal. The data reinforce this notion, and reveal that 57% of intercourse was logged on fertile days.”

Many participants used withdrawal as their form of “birth control” when having intercourse on fertile days. However, this is not an accepted form of pregnancy prevention and could skew the data, as some participants may have considered this approach to be correct use of the app. Additionally, 52.8% of participants reported using condoms during the fertile window. Although Natural Cycles classifies this as correct use of their app, if pregnancies occurred during those cycles, this would reflect the failure of the condom and not a natural method.

In summary, true adherence with the method and reporting was likely relatively low among users in the US cohort. Further studies with more controlled conditions and more active participants may yield more promising results and provide evidence for what could be an effective and simple form of family planning. Until then, the study results from perfect use may be encouraging for women who desire effective non-hormonal, non-invasive family planning.

References

[1] Pearson JT, Chelstowska M, Rowland SP, et al. Contraceptive Effectiveness of an FDA-Cleared Birth Control App: Results from the Natural Cycles U.S. Cohort. J Womens Health (Larchmt). 2021;30(6):782-788. doi:10.1089/jwh.2020.8547

ABOUT THE AUTHOR

Madison Hoover

Madison Hoover is a fourth-year medical student at Philadelphia College of Osteopathic Medicine in Suwanee, Georgia. She completed her undergraduate education at the University of Georgia in Athens, GA. She plans to pursue residency in family medicine and is interested in women’s health and LGBTQ+ medicine. She enrolled in the FACTS elective to gain a deeper understanding of reproductive health and provide patients with more options for reproductive health and family planning.

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