• Ava monitors physiological parameters that are correlated with changing reproductive hormone levels. Ava’s algorithms use the data gathered continuously throughout the night to detect a woman’s fertile window.

  • 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 under the lead of Prof. Dr. Brigitte Leeners, the leading expert on the mathematical modeling of menstrual cycles.

  • Ava is CE certified and approved by the FDA.

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What Ava measures

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.

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. 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 reading (when taken at a room temperature of 64.5 – 77 degrees Fahrenheit) are between 90.5 – 98.2 degrees Fahrenheit.

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.

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 4 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.

Our Clinical Study

Ava was tested in a year-long clinical study at the University Hospital of Zurich under the lead of Prof. Dr. Brigitte Leeners, a leading expert on the mathematical modeling of menstrual cycles. 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 Ava’s clinical studies 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. Our 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.

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 phase. 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 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 24 – 35 days in a user-friendly, accessible, and affordable package.

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Our Medical Team


Prof. Dr. med. Brigitte Leeners

Scientific Advisory Board


Lisa Falco, PhD

VP Data Science


Prof. Dr. Elena Gates

Medical Advisor


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