What Ava measures
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 than oral temperature, but we found that it exhibits the typical biphasic pattern during the cycle.
Average skin temperature readings (when taken at a room temperature of 64.5 – 77 degrees Fahrenheit) are between 90.5 – 98.2 degrees Fahrenheit.
Average skin temperature readings (when taken at a room temperature of 18 – 25 degrees Celsius) are between 32.5 – 36.8 degrees Celsius.
How often your heart beats per minute at rest.
Scientific literature shows that resting pulse rate is lower during the follicular phase than the luteal phase. Ava’s clinical research partner, the University Hospital of Zurich, identified further variation in resting pulse rate throughout the menstrual cycle: resting pulse rate rose by about 2.1 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.
Rate of respiration per minute.
Scientific literature shows that breathing rate is higher in the luteal phase than in the follicular phase. Breathing rate can vary widely during the course of a day due to your activities, but typical breathing rates during sleep are much more stable, and range from 10 – 25 bpm.
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.
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.
Ava tracks your movement with an accelerometer.
This parameter allows Ava to distinguish between light and deep + REM sleep.
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.
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.
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 records the amount of sleep you get each night. Additionally, Ava tracks the percentage of combined deep and REM sleep. Deep sleep is important for feeling rested the next morning, while REM sleep is important for learning and storing memories.
Typical sleep cycles for adults include 50 – 65 percent light sleep and 35 – 50 percent deep sleep + REM.
Ava must be worn for at least four hours per night with three hours of sleep in order 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, 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.