How Ava works

How the Ava bracelet detects the fertile window

How Ava works 2017-04-19T07:40:08+00:00

The Ava Fertility Tracker is for women who want to monitor their health for trying to conceive or getting to know their bodies.

The Ava bracelet is a completely unprecedented method of tracking a woman’s cycle and health. While you’re sleeping, Ava’s sensors collects data on nine different physiological parameters. These parameters are fed into our algorithm in order to detect your fertile window, physiological stress level, sleep quality, and more.

Other methods of fertility tracking rely on only a single parameter, and thus cannot provide a complete picture of your fertility in real time. Ava detects the very first signs that the fertile window is beginning, and confirms when it ends.

And because Ava is a wearable device, it provides accurate information about your cycle with  minimal user effort. Wear Ava when you sleep, and wake up to insight.

  • Ava has been shown to detect an average of 5.3 fertile days per cycle at 89% accuracy
  • Ava was clinically tested in a year-long study at the University Hospital of Zurich.

  • Ava is an FDA registered device and CE certified

A new way to track


Ava is worn every night while sleeping, when the body is completely at rest and your physiological parameters are not influenced by activity.


Sync the Ava bracelet with the app every morning.


See insight about your menstrual phase, sleep, stress and resting pulse rate. During pregnancy, also monitor weight and physiological progress.

What Ava measures

A note about reading your data

Ava works differently than other fertility tracking methods you may have used in the past. You may be surprised when you look at your Ava data and don’t see an obvious temperature spike after ovulation or a clear pattern in your resting pulse rate.

Other methods predict your fertility based on one or two factors, but Ava combines signals from nine different parameters, resulting in greater accuracy. This holistic approach enables Ava’s algorithm to distinguish signals from noise—to recognize whether an increase in pulse rate, for example, is due to impending ovulation or simply stress.

So if your data on Ava appears to be all over the place, don’t worry! While it may not make sense to the human eye, it makes sense to our algorithm and is reflected in your fertility predictions.

How often your heart beats per minute at rest.

Resting pulse rate is lower during the follicular phase than the luteal phase. Ava’s clinical study identified further variation in resting pulse rate throughout the menstrual cycle: resting pulse rate rose by about three beats per minute at the beginning of the fertile window. During pregnancy, resting pulse rate remains elevated.

Typical resting pulse rates are between 40 and 80 bpm. If you are very physically active, your resting pulse rate may be even lower than 40 bpm. Stress, illness, and alcohol can cause temporary increases in resting pulse rate.

The temperature of your skin at your wrist.

Skin temperature is one of the parameters Ava uses to identify your fertile window. It rises by about one half of a degree after ovulation, and remains elevated until your next period begins. During pregnancy, temperature remains elevated.

If you’ve ever tracked your basal body temperature orally, you’ll notice that Ava’s temperature reading is several degrees lower than your oral temperature. It’s normal for skin temperature to be lower and more variable than oral temperature. /

Average skin temperature readings (when taken at a room temperature of 64.5 – 77 degrees Fahrenheit) are between 90.5 – 98.2 degrees Fahrenheit./

For Celsius:

Average skin temperature readings (when taken at a room temperature of 18 – 25 degrees Celsius) are between 32.5 – 36.8 degrees Celsius./

The lower your HRV ratio, the less stressed you are.

HRV is the variation in the time interval from one heartbeat to the next. It can be used as an indicator of physiological stress: when there is a lot of variation in the time interval between heartbeats—high HRV—it means you are more resilient and less stressed. Ava measures the ratio between low frequency and high frequency waves in your heart rate. Because Ava measures HRV using this ratio, a lower number means you are less stressed.

Normal HRV ratio varies widely from person to person, but by looking for an increase or decrease from your baseline HRV ratio, you can learn about your body’s physiological stress level.

Total sleep hours and ratio of light to deep + REM sleep.

The quality and quantity of sleep you’re getting each night are important parameters to track for your fertility. Your menstrual cycle can affect your sleep, and your sleep, in turn, can affect your menstrual cycle. Pregnancy can also influence sleep.

Ava tracks the amount of sleep you get each night. This doesn’t count time you might spend reading in bed; Ava can distinguish between sleeping and lying quietly . Ava also tracks the percentage of light sleep and the percentage of combined deep and REM sleep.

Typical sleep cycles for adults are 50 – 65 percent light sleep and 35 – 50 percent deep sleep + REM.

You need at least four hours of consecutive sleep in order for Ava to work properly.

Ava measures the physiological changes that happen when your body is completely at rest. It takes at least four hours for these parameters to stabilize and for Ava to get an accurate reading. If Ava recorded less than four hours of sleep, it won’t use the data from that night in calculating your fertility.

If you wore Ava for more than four hours but are still seeing “data quality poor,” it could mean the battery died during the night or that the sensors lost contact to your skin. Make sure Ava is fully charged when you put it on. This is indicated by a green light on the top of the bracelet.

The process of supplying blood to the tissues of your body.

As blood flows through your capillaries, it delivers nutrients to the tissues and helps sweep away waste. Then, the blood flows back to the heart, and begins the process all over again.

If you’ve ever had an elastic band around your finger and felt the blood flow being cut off, you’re already familiar with the process of perfusion. While you can limit perfusion with an elastic band, perfusion can also change naturally for different reasons. For example, your perfusion changes in order to keep you warm or cool you down. Perfusion also changes in relation to the menstrual cycle: it is higher in the fertile days and lower during the luteal phase.

Rate of respiration per minute.

Ava tracks your movement with an accelerometer.

This parameter allows Ava to distinguish between light and deep + REM sleep.

Heat loss is closely related to the onset of sleep.

As you lose heat through your hands and feet, your skin temperature increases and your core body temperature decreases.

Heat loss is also related to your metabolic rate. The mechanism for the maintenance of the higher temperature during the luteal phase is still a matter of scientific discussion. Some researchers believe that reduced heat loss is responsible, while others believe that higher internal heat production (increased metabolic rate) is the cause.

Bioimpedance measures the resistance of body tissue to tiny electric voltages.

This parameter provides information about the skin, including hydration and sweating patterns. As you have probably observed throughout your life, reproductive hormones have an impact on your skin. Your skin can change at different phases of the menstrual cycle, during puberty, and during pregnancy.

The science behind Ava

Using physiological parameters to track a woman’s cycle and health

Ava is the first product to use sensor technology to precisely detect the fertile window in real-time.

Most fertility monitoring products are based on a single parameter, providing an incomplete picture of the user’s fertility status. These parameters include basal body temperature, and urinary LH. Used alone, none of these methods is able to accurately detect both the beginning of the fertile window and confirm ovulation. Furthermore, the reliability of a single parameter may be compromised by confounding factors. For these reasons, many women use multiple fertility tracking methods simultaneously, a tedious and time consuming process.

Ava tracks multiple physiological parameters that correlate with fertility, removing the need for the user to track multiple parameters herself while also providing more accurate predictions.

Clinical Study

Ava was tested in a year-long clinical study at the University Hospital of Zurich. The prospective observational study tracked 37 healthy, non-pregnant women, between 20-40 years old. Ava was found to detect an average of 5.3 fertile days per cycle, at 89 percent accuracy.

Results from the clinical study identified multiple physiological parameters that correlate with both the rise in estradiol that precedes ovulation as well as the rise in progesterone that follows ovulation. Ava has protected these methods with multiple patent applications. The scientific results have been presented at congresses in the USA, Germany, and Switzerland. We are submitting our latest findings for publication in peer reviewed scientific journals, beginning with a paper tackling the correlation between pulse rate and the fertile window. In addition, several more publications are in the pipeline detailing how the different parameters Ava measures correlate with the menstrual cycle.

The correlation between pulse rate and the fertile window

Earlier clinical studies demonstrated that there is a significant elevation in pulse rate measured in the clinic during the fertile window compared to the menstrual phase1. Ava conducted a prospective observational clinical trial to test whether wrist worn Photoplethysmography (PPG) sensors could reproduce this clinically observed association. Indeed, the results from our clinical trial indicate that pulse rate measured with wrist-worn PPG sensors is significantly elevated compared to the pulse rate during the menstrual phase. The advantages of using wearable sensors are numerous, including the ability to continuously monitor the pulse rate during sleep thus minimizing the interference imposed by the various daily activity.

Our clinical trial also showed that the correlation between pulse rate and the different menstrual phases was robust to a broad range of activities the participants engaged in before sleep.

Most importantly, Ava has developed algorithms that allows us to detect the fertile window even for individuals with highly variable cycle length, a feature that is not attainable using the calendar method.

In conclusion, Ava offers science-backed fertile window detection that is suitable for a range of users with cycle lengths between 21 – 35 days in a user-friendly, accessible, and affordable package.


The Team

The Ava team brings together industry leaders in wearable technology, women’s health, and data science to deliver an unprecedented device for monitoring women’s health.

Prof. Dr. med. Brigitte Leeners

Scientific Advisory Board

After medical studies at the University of Aachen/Germany, Prof. Leeners became a senior physician at the University of Zurich/Switzerland. One of her main research topics is mathematical modelling of the menstrual cycle. Prof. Leeners’ research has been published in leading publications in the field of gynecology and reproduction medicine around the world. Prof. Leeners has been strongly involved in the scientific studies of Ava, and joined the scientific advisory board in 2015.

Lisa Falco, PhD

VP Data Science

After an MSc in Engineering Physics from Chalmers University of Technology in Gothenburg/Sweden, Lisa did a PhD in biomedical signal processing at EPFL in Lausanne/Switzerland and was a visiting researcher at Harvard Medical School in Boston/US. Lisa worked in the algorithm and signal processing teams of Solianis (non-invasive measurement of blood sugar) and Scanco Medical (microcomputed tomography scanners). Lisa is the author of several patents and has presented scientific results at various international conferences.


Frequently Asked Questions

I have irregular cycles. Can I still use Ava? 2016-12-30T21:23:05+00:00

As long as your cycles tend to fall within 24 – 35 days, you can still use Ava. Future versions of Ava will support more irregular cycles.

How accurate is Ava? 2016-12-30T21:23:47+00:00

Ava was shown in a year-long clinical study to recognize an average of 5.3 fertile days per cycle, at 89 percent accuracy.

Can Ava be used to prevent pregnancy? 2016-12-30T21:24:16+00:00

No, Ava cannot be used for contraception. Since our focus is helping women get pregnant, our algorithm identifies the most fertile days of the cycle. For a contraceptive product, we’d want to also identify days where it’s unlikely but still possible to get pregnant.

That said, if you’re practicing NFP or FAM, Ava could be a great complementary tool.


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Jade & Tanner Got Pregnant with Ava!

Thank you everyone for all the support and for sharing your stories since we announced our pregnancy on Wednesday! We are so excited! For those of you who have been following us for a while, you may have seen our past post back in November about using the @avawomen bracelet to help us get pregnant faster. We got pregnant really soon after we started using Ava! I wore the bracelet every night while sleeping and Ava told us which five days were the best days to try for a baby each month. It took so much stress out of the process and was so easy to use. Since so many of you have kindly opened your hearts to me and have shared your stories about trying to get pregnant, I wanted to share what worked for us. Also, I've partnered with Ava to get you all a $20 off coupon code: JANNERBABY I'll be using Ava for all our future pregnancies and cycle tracking between babies. Thank you, Ava.