What Ava measures
How often your heart beats per minute at rest.
Heart rate is known to increase progressively during pregnancy until delivery . This is accompanied with a gradual increase in blood volume, red blood cells mass, and stroke volume. The majority of the extra blood is directed to the uterus, breasts, and kidneys to accommodate the complex ever changing hormonal environment that occurs during the pregnancy.
 Thornburg, Kent L., et al. “Hemodynamic changes in pregnancy.” Seminars in perinatology. Vol. 24. No. 1. WB Saunders, 2000
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 than oral temperature, but we found that it exhibits the typical biphasic pattern during the cycle.
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.
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.
The lower your HRV ratio, the less stressed you are.
Ava measures the ratio between low frequency and high frequency waves in heart beats. A lower value corresponds to a lower level of stress. 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 health and pregnancy. You will notice your sleep pattern changing throughout your pregnancy.
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. Pregnant women might sleep longer, have fewer periods of deep sleep and wake up more often during the night [1,2].  Lee, Kathryn A., and Caryl L. Gay. “Sleep in late pregnancy predicts length of labor and type of delivery.” American journal of obstetrics and gynecology 191.6 (2004): 2041-2046.  Lee, Kathryn A., Mary Ellen Zaffke, and Geoffry McEnany. “Parity and sleep patterns during and after pregnancy.” Obstetrics & Gynecology 95.1 (2000): 14-18.
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 needs to be worn 4 hours each night in order to work and display you your data.
As for the data quality of the parameters measured: Ava measures the physiological changes that happen when your body is completely at rest. It takes at least three hours of sleep for the parameters to stabilize and for Ava to get an accurate reading.
The process of supplying blood to the tissues of your body.
Perfusion is 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.
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.
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.