A Summary of Research Findings

By Matthew Thigpen, MD
October 23, 2019

Editor’s Note: This is a review of research[i] published in 2016 about the effectiveness of cycle computers to indicate the fertile and infertile phases of the menstrual cycle. It was written by a medical student as part of a two-week online elective taught by FACTS executive director, Dr. Marguerite Duane, at Georgetown University College of Medicine. This study joins the expanding body of research assessing devices, apps, and other female technology (fem-tech) growing in popularity as women seek non-hormonal ways to plan their families and monitor their health.


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With the rising interest in alternatives to conventional methods of birth control as well as advances in technology to monitor signs of fertility, cycle computer monitors are a potential new avenue to assist women to achieve pregnancy and for people wishing to prevent pregnancy. These monitors, such as LadyComp, Pearly, and Daysy, utilize an internal statistical database and daily basal body temperatures to determine the fertile and infertile times of a woman’s cycle. By using the algorithm and temperature to tell users their fertility status, the developers of these monitors hope to avoid some of the potential for human error that may limit other methods of natural family planning.

The primary aim of this study was to determine the effectiveness of using cycle monitoring computers to prevent pregnancy. Additionally, the study was expanded to observe the potential for these monitors to predict whether a child in the womb is male or female.

Between May and June of 2016, surveys were sent to people who had purchased one of the cycle computers available in Poland at that time. Respondents were randomly selected from a database maintained by VE Valley Electronics GmbH, a distributer of cycle monitors. Of the 3,450 surveys sent, 361 women returned questionnaires completed accurately, leading to 17,322 cycles reported.

The survey consisted of six questions to determine eligibility. Responses were excluded from participants who used the computer for less than 12 cycles, used other contraceptive methods, or did not always follow the computer’s indications. The other questions in the survey sought to determine unintended pregnancy rates and the accuracy of determining the sex of the child. From this data, the survey sought to determine the Pearl Index, a measurement of contraceptive efficacy, for the cycle computers when used correctly.

Of the 361 respondents, 177 surveys met the eligibility criteria for use when determining the Pearl Index. These 177 surveys provided 10,423 cycles of data and had an unintended pregnancy rate of 4. Using this data, the study determined a Pearl Index of 0.499, placing it on a par with other methods of contraception such as hormonal based methods. With perfect use, this roughly equals 1 unintended pregnancy per 200 women over the course of a year. Of the respondents, 28 women used their cycle computer to forecast the sex of their child. The prediction was correct for 20 of the respondents (71.4%).

Based on the low rate of unintended pregnancies across a large number of cycles, these monitors show promise as an effective method of natural contraception. Alongside the potential efficacy of this method, the use of quantitative data in the form of temperature measurement also provides a more standardized approach that could allow for more consistent outcomes in research of natural fertility planning methods. The models designed to predict the sex of a pregnancy also showed reasonable efficacy but would benefit from a larger study population.

Overall, this study added to the foundation of data for use of cycle monitors as a means to avoid pregnancy. While these monitors typically range from 300 to 500 dollars depending on the model, this is still comparable to the annual cost of many of the hormonal methods of contraception. Since these monitors can be used for years and may be partially covered by insurance, these devices could provide a less expensive alternative without the side effects of hormonal contraception. These monitors may also appeal to women and couples who are seeking a fertility awareness based method but would like to have a display report their fertility status.

[i] Demiańczyk A, Michaluk K. Evaluation of the effectiveness of selected natural fertility symptoms used for contraception: estimation of the Pearl index of Lady-Comp, Pearly and Daysy cycle computers based on 10 years of observation in the Polish market. Ginekologia polska. 2016;87(12):793-7.

Author Bio: Matthew Thigpen, MD is a family medicine resident at Texas Tech Amarillo. He was a 4th year medical student at Texas A&M College of Medicine when he completed this review. He is “thankful for the opportunity to get a broader perspective on the research and risks of the various methods of family planning through the FACTS elective.”

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