illustration of a strain from a dna helix with 3 icons of pmdd

Illustration: Katrin Friedmann

Temps de lecture : 12 min

The science of your cycle: evidence-based app design

Everything we do at Clue is based on two complementary foundations — the most current research and user-generated data.


Health and fitness is one of the fastest growing categories of apps, as people are finding new ways to track and new things they’d like to discover about themselves.

Period tracking is the oldest form of “quantified self.” This started long before paper or electronic gadgets were around. If you search for “period tracker” today, you’ll find over 200 apps available on iOS and Android combined. Period trackers are the second largest category of apps in health and fitness, second only to running apps. Despite their focus on health, most of these apps have been created without involvement of doctors or scientists from the field of biomedicine.

The Clue team has worked hard to be recognized as a leader in the scientific approach to tracking. Over 100 pages worth of scientifically valid information about menstrual health is included in Clue, providing our community of users with extensive opportunities to learn new facts about the cycle. In addition, Clue’s scientific collaborations include partnering with academic institutions to advance female health globally.

This is the story of how we have done it so far, and how we intend to transform reproductive healthcare in the future.

About Clue

Our mission is to help people gain insights about their body and manage their menstrual health and fertility. We inform people about sex and reproductive health, because there are wildly varying levels of sex education around the world and a pervasive lack of basic knowledge about reproductive health (1–4).

Clue aims, through collaboration with top academic institutions, to expand our base of knowledge about human reproductive health on a global level. This will in turn enable Clue’s community of users to get better information, better predictions and empower them to make better decisions about their health.

About the menstrual cycle

The menstrual cycle is a vital sign of overall health. Changes in the cycle may indicate an underlying medical condition, so it’s important to closely track frequency, duration, intensity and other characteristics. When we think about the menstrual cycle we often only think about our period, but the period is only a smart part of our cycle. The rest of the cycle deserves the same attention. In addition to planning or avoiding pregnancy, people want to plan their everyday activities around their cycle, so their lifestyle is not interrupted.

An individual’s menstrual cycle is characterized by high variability in cycle length (21–35 days), depending on age, genetics and lifestyle (5, 6). According to scientific literature, menstruation lasts an average of 4–6 days (5) and the fertile window usually starts 5 days before an individual ovulates (6).

On average, individuals will experience ~400 menstrual cycles/periods during their lifetime (7), depending on the events like pregnancy and chronic illness.

All people falling within this “average” will experience the usual phases of the menstrual cycle:

  • The follicular phase starts during the period, and is the phase of the egg-containing follicle growth, which leads to and ends with ovulation, when the mature egg is released from the follicle and is ready for fertilization.

  • Ovulation is the shortest event in the entire menstrual cycle, and it marks the end of the follicular phase and the beginning of the luteal phase.

  • In the luteal phase, leftovers of the now-empty follicle stay attached to the ovary and start producing and releasing progesterone (the structure is called the corpus luteum). This phase is meant to help the uterus to prepare for pregnancy.

In healthy conditions the corpus luteum will degenerate and stop producing progesterone, unless there is a signal from an implanted embryo (through increased levels of yet another hormone, HCG-human chorionic gonadotropin) (6). As the corpus luteum gets smaller there is a change in the ratio between estrogen and progesterone, and another molecule, prostaglandin, which is leading to the onset of the period.

About taboos of the menstrual cycle

The menstrual cycle is typically either an uncomfortable or a taboo topic in many cultures (1–4, 8, 9). Moreover, the “facts” sometimes heard in popular culture about the menstrual cycle, period and PMS are often misleading or simply wrong. Cultural and societal discomfort when talking about anything period related makes it difficult to gain access to valid information, even if it is urgently needed. When lacking knowledge, most people wait until they experience a problem or until pregnancy occurs to get information about the basics of reproductive health. Even then, rather than talking about it to their healthcare providers, people often revert to online mass media and dubious forums — which often propagate invalid information.

Clue bypasses cultural discomfort by speaking plainly, and refusing the use of euphemisms. Sex is called “sex,” not “the baby dance.” Menstrual bleeding is called “bleeding,” not “Aunt Flo.”

About individual needs

A person needs to understand that the cycle is fundamental to one’s health and well-being. Increased self understanding enables us to plan and live our lives with as few surprises as possible, and identify potential health issues before they become problems.

When we track the cycle and have access to predictions, we’re no longer waiting for something to happen to us. Instead, we’re actively taking back our identities from this event that has been used to define our roles, experiences and lives. It’s a radical idea.


Clue is a utility designed for each person to track and learn about their own unique cycle, at any point in their reproductive lifespan. Clue cuts through pervasive misinformation by building upon the most current peer-reviewed bio-medical research on the menstrual health and fertility. This work was done in collaboration with academic researchers and scientists, medical healthcare professionals, as well as business people and most importantly, Clue’s community of everyday users.


App design process

Clue’s design process was based on three principles: increased user happiness, rapid data entry and to facilitate the discovery of accurate insights.

Rationale for these principles:

(I) Happiness: the cultural norm about the menstrual cycle is awkwardness, going so far as to pretend as if the period doesn’t exist. We aimed to make people feel comfortable about their period, as it is a normal, healthy and common biological process.

(II) Rapid data entry: making Clue easy to use, consequently increasing compliance and finally collecting more accurate research-grade data. This leads directly to:

(III) Accurate insights: people receiving insights about their cycle are able to understand their cycle better, and are in turn aware that tracking more data will lead to further discoveries about their body. This is the virtuous cycle of tracking.

Easy to read scientific text

Clue contains about 100 pages of simplified, scientifically valid text that covers the basics of the menstrual cycle and reproductive health. Clue’s text directly answers the most asked questions, such as “am I healthy, and am I normal,” and goes further to answer questions people ask after gaining a more comprehensive foundation of basic knowledge. Clue’s informational text is based on up-to-date research from peer-reviewed scientific publications. Clue’s text starts with easy-to-understand summaries, leading deeper into the supporting biomedical insights and ends with a list of references from peer-reviewed publications that validate all claims made.

The informational text is distilled from numerous publications and is written by scientists working for Clue. Clue’s text goes through multiple editorial reviews. The first review of Clue’s text results in accuracy, ensuring that all claims are backed by peer-reviewed research. The sources for claims are referenced clearly at the bottom of all sections of text, and can be found in the PubMed database.

A second review of Clue’s text by medical doctors and gynecologists reflects what they experience in their practices and results in everyday common sense. A third review of Clue’s text ensures that all previous edits have resulted in text that’s still easy to read by a mainstream audience. Fourth, fifth and sixth edits of Clue’s text occur when the text is translated into a new language. That text is professionally translated, reviewed by a professional with medical background, then finally reviewed by Clue’s community of users to ensure an accessible tone of voice.


Clue’s algorithm is built to estimate the occurrence of the next period, fertile window and PMS, helping users to predict actual physiological processes occurring in the body throughout the cycle. Clue users have a choice to track diverse data.

Clue’s data scientists are regularly improving predictions by integrating additional data points (including moods, pain, sleep, etc.) into Clue’s predictive algorithm. This will enable Clue to provide better predictions not only the period and moods, but ovulation too. This should be a minimum requirement for any service that claims to identify when ovulation occurs, when one’s next period will start or when one can get pregnant. Clue only makes conclusions based on scientific validation.

Everything we do at Clue is based on two complementary foundations — the most current research and user-generated data.

We iterate between these to improve the individualized predictions given to each of Clue’s users. Before Clue’s algorithm has had a chance to learn about each individual user, the starting estimates are based on averages from medical literature. The more and longer a user tracks their data, the more the algorithm learns, and is able to provide better predictions, becoming more valuable.

We are also able to assess just how well the algorithm is performing in predicting different aspects of users’ cycles by testing new models against the longitudinal data sets of Clue users. This enables us to pose and test hypotheses, bringing about not only more accurate predictions that can be fed back into evolving the algorithm, but also learnings and insights on important issues affecting a smaller percentage of our users not addressed elsewhere.

Scientific collaborations

Our up-to-date knowledge of the cycle comes from partnerships with top-tier universities such as Columbia, Harvard and Stanford. We collaborate on prospective studies to answer different questions on reproductive health.

Our tracking categories, info text and algorithm are constantly evolving. They are based on medical literature as well as data generated from our user base. In the long term, the vast longitudinal data sets users generate will support academic and clinical research studies, and result in insights to improve female health globally.

The Clue team directly engages in a mass qualitative research effort every day that builds upon our knowledge of user needs and expectations. This research effort starts every time a user contacts us with a support question.

User support

Clue support is provided by a wide range of people, including scientists, engineers, designers and marketers. This ensures the entire organization develops a comprehensive empathetic relationship with Clue’s community of users. This empathy allows the Clue team to create a constantly improving user experience and to ensure compliance with data collection.


Today Clue has more than 4 million users in over 180 countries tracking their cycles for a wide variety of reasons (as of October, 2015). Every day, people reach out to let us know that they have conceived, diagnosed diseases and improved their lives with the help of Clue.

We are contacted by world renowned institutes thanks to our serious and “no bullshit” approach to this delicate, but common, aspect of people’s lives.

With the help of academic collaborators and our users, we have identified ~30 important tracking categories. Significantly, in >80% of the cases, the symptoms that users desired to track were nearly identical to the symptoms verified across all Clue’s accumulated research.

The emotional connection created by Clue’s design results in a remarkably high retention of active users. People tend to track more data when the experience is positive, easy and enjoyable. As a result, more and better data sets are created.

It’s most important to us that Clue’s community of users continue to discover insights about their own cycles. Some of these insights have dramatically improved their quality of life, such as identifying PCOS earlier than they otherwise would have. We can help a user identify what’s typical for them based on personal analytics they can bring to their healthcare provider, rather than only comparing their personal averages to global statistics. This can help some people who believe they have “extremely irregular” cycles when they actually don’t.

With the basic knowledge of fertility provided by Clue, such as when the fertile window and ovulation are actually occurring, people have the ability to get pregnant more quickly (≤ 3 months, as reported by our users). Beyond and before pregnancy, there also seems to be no end to the desire to identify patterns and be alerted of potential events before they happen, be that for planning holidays, significant life events, exercise or important business meetings.


(I) Clue is a frontrunner in solving the societal problem of the lack of availability of basic reproductive knowledge. This was revealed by market research and our own customer support conversations. Clue has proven to be an excellent pocket guide to help answer questions both at the level of global statistics, and also that of personal analytics.

(II) Good design and an enjoyable user experience increases compliance of self-reported data.

(III) Clue is designed to be useful for every person from premenarche through to menopause. We hope this creates a vast longitudinal data set to carry us towards our vision of improving healthcare for individuals create advances for female health globally.

(IV) Clue is created using evidence-based approach. This makes Clue ideal for integrating with academic and clinical research. We are successfully drawing positive attention from of practitioners, researchers and academics, from the diverse communities of medical professionals to business and design.

Future perspectives

With a user base 1,000–10,000 times larger than sample sizes of most completed research studies — and growing larger by the day — Clue is already able to contribute to advances in global health research. We will be able to test results from existing research through studies using global population, covering a longer timeframe and with a couple of magnitudes larger number of participants than previous studies. We will also have a very detailed, unique perspective on symptoms and cycle characteristics experienced by people with e.g. polycystic ovary syndrome (PCOS), heavy menstrual bleeding (HMB), endometriosis or premenstrual dysphoric disorder (PMDD); the knowledge gained from studying these conditions will be fed back into the algorithm to provide the value back to the users.

Who are the people of Clue?

Our team is composed of diverse people with the common goal of bringing human reproductive healthcare education into the homes of people that need it. We are from more than 10 different cultures around the world, genetic makeups and educational backgrounds. What we share in common is a sincere striving to do good in the world. We are not afraid to talk about our hopes and fears amongst each other. This enables us to be honest, empathic and genuine to our users, who we all consider to be a part of the Clue team.

une illustration de la fleur de Clue
une illustration de la fleur de Clue

Vivez en symbiose avec votre cycle en téléchargeant l'app Clue maintenant.

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