The Science Behind Ava
- 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, a leading expert on the mathematical modeling of menstrual cycles.
- Ava is an FDA Class 1 medical device.
What Ava Measures
Average skin temperature reading (when taken at a room temperature of 64.5 – 77 degrees Fahrenheit) are between 90.5 – 98.24 degrees Fahrenheit. If you sleep in a room warmer than 77 degrees it could cause your skin temperature to go up.
Most people think of heart rate as the average number of beats per minute, but your heart rate changes from beat to beat. HRV measures this naturally occurring irregularity in heart rate. The more variation in the interval between beats, the lower your physiological stress level.
Ava measures the ratio between low frequency and high frequency waves in your heart rate. Scientific studies have shown that the HRV ratio is a good indicator to assess the balance between the sympathetic nervous system and the parasympathetic nervous system. An imbalance in these systems—usually when the sympathetic branch takes the upper hand—is associated with high physiological stress level and results in a high HRV ratio.
Estrogen and progesterone have an impact on HRV. The HRV ratio is increased during the luteal phase when progesterone peaks, compared with the follicular phase, when estrogen is high.
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. HRV ratio is complicated, but the important thing to remember that a higher HRV ratio indicates higher stress.
Average percentages for adults are 47 – 60 percent light sleep and 33 – 48 percent deep sleep + REM.
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. Estrogen and progesterone also have an influence on perfusion. Estrogen increases perfusion, while progesterone has the opposite effect.
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 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.
Our Clinical Study
Ava completed 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. Ava was found to identify an average of 5.3 fertile days per cycle with an accuracy of 89 percent. Read a summary of our clinical study.
The clinical study used a wearable device to track nine physiological parameters throughout 155 menstrual cycles. The data gathered was cross referenced with urine tests taken during the fertile phase.
The results of the study were presented in June 2016 at the Swiss Society of Obstetrics and Gynecology Annual Congress and in October at the German Society of Obstetrics and Gynecology Annual Congress. Bayer, the leading women’s health company, is sponsoring Ava’s presentation.
Our scientific research paper will be submitted in summer 2016. We expect it to be published by a leading peer-reviewed journal in reproductive health by the end of 2016.
Ava is planning further clinical studies to refine its algorithms for use in both pregnancy recognition, pregnancy monitoring, and possible use as a non-hormonal contraceptive device.
How physiological parameters can be used to identify fertile days.
There are only a few days per cycle when it is possible for a women to conceive. These days vary from woman to woman and from cycle to cycle, but studies show that this time usually lasts six days, beginning five days prior to ovulation and lasting until the day of ovulation itself.
Not all women experience six fertile days. The fertile window is impacted by:
- The lifespan of the egg, which is up to 24 hours after ovulation
- The lifespan of the sperm. The median is 1.5 days, but when fertile-quality cervical mucus is present, some high-quality sperm can survive up to five days.
The fertile window begins with a gradual rise in estradiol levels over three days1, along with a moderate probability for conception. The two days that follow are characterized by high levels of estradiol in combination with a surge in luteinizing hormone. These two days, along with the day of ovulation, represent peak fertility, with a pregnancy probability of more than 20 percent. Seventy percent of pregnancies are conceived in these latter three days of the fertile window.
After ovulation, the likelihood of conceiving drops rapidly due to the limited lifespan of the follicle (typically 12-24 hours).2
Tracking physiological parameters associated with the rise in estradiol allows women to recognize the first days of the cycle when conception is possible, and provides advance warning of peak fertile days. Research shows that women who track their fertile days are twice as likely to conceive in a given month (compared with untimed intercourse once per week). 3
The rise in estradiol levels stimulates the secretion of fertile quality cervical mucus, which supports the survival and transport of sperm. Intercourse that occurs after estradiol levels rise may lead to conception, as some sperm can survive for several days in favorable environments.
Changes in reproductive hormone levels have measurable physiological impacts throughout the body. 4 For example, it has been understood for decades that progesterone has a direct impact on basal body temperature 5, causing a BBT spike by one half to one degree Fahrenheit after ovulation. Charting temperature with a BBT thermometer has been shown to be a moderately effective method for detecting when ovulation has occurred.
Advancements in sensor technology make it possible to collect physiological data points continuously over long periods of time, enabling more precise monitoring of correlations between the hormones progesterone and estradiol with physiological parameters. The Ava fertility tracker is the first fertility tracking device to collect data continuously throughout the night, allowing it to detect an average of 5.3 fertile days per cycle with minimal user effort.
- Fritz 2012 ↩
- Wilcox 1996 ↩
- Wilcox AJ, Weinberg CR, Baird DD. Timing of Sexual Intercourse in Relation to Ovulation. Obstet Gynecol Surv. 1996;51(6):357-358. doi:10.1097/00006254-199606000-00016. ↩
- Hirshoren N, Tzoran I, Makrienko I, et al. Menstrual cycle effects on the neurohumoral and autonomic nervous systems regulating the cardiovascular system. J Clin Endocrinol Metab. 2002;87(4):1569-1575. doi:10.1210/jc.87.4.1569. ↩
- Kräuchi K, Konieczka K, Roescheisen-Weich C, et al. Diurnal and menstrual cycles in body temperature are regulated differently: A 28-day ambulatory study in healthy women with thermal discomfort of cold extremities and controls. Chronobiol Int. 2014;31(1):102-113. doi:10.3109/07420528.2013.829482. ↩