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When Am I Most Fertile?

Timing intercourse is essential for conception because conception can only happen during the fertile window, which is typically the 5 days leading up to ovulation and the day of ovulation (Wilcox).

Peak fertility is the 2-3 days prior to ovulation (American Society for Reproductive Medicine). After ovulation occurs, it is no longer possible to get pregnant until the next cycle (Wilcox).

To accurately identify this fertile window, Priya uses continuous core body temperature (CCBT). CCBT can reliably detect subtle changes in temperature patterns that occur prior to ovulation. 

“Identifying the fertile window is a key element to conception. The fertile window can occur much earlier or later in the cycle than the clinical guidelines may suggest.”


“Peak fertility is found to be the 2-3 days prior to ovulation, so using the basal body temperature shift after ovulation is likely too late when trying to conceive. ”

American Society for Reproductive Medicine

Priya Clinical Study Results

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Preliminary clinical study data shows that the Priya Personal Fertility System predicts ovulation on average 2.6 days prior to the luteinizing hormone (LH) surge as shown in the graph above (clinical PT-004 data on file). 

How Continuous Core Body Temperature Predicts Ovulation

We have nearly 3.5 trillion clocks called circadian rhythms in our bodies that regulate our organs, weight, sleep, and fertility. Who knew?! Core body temperature (CBT) has been studied and shown to be a highly reliable marker for circadian rhythm patterns (Brown). These patterns correlate with the release of hormones, such as estrogen and progesterone.

So what do circadian rhythms have to do with fertility? Allow us to elaborate. Circadian rhythm patterns change with the phases of the menstrual cycle, allowing ovulation prediction by detecting those patterns, best seen through continuous core body temperature (CCBT) monitoring.

Here’s where we come in to help. Priya records CCBT, which, combined with the application of the unique Priya algorithm, identifies subtle temperature patterns, undetectable by standard oral or skin thermometers, that occur prior to ovulation (Coyne, Cagnacci).

When measured accurately, this temperature shift provides a powerful tool for predicting ovulation; having intercourse during these pre-ovulatory days significantly increases the probability of conception (Dunson).

priya sensor and app

How Does Priya Compare to Other Methods to Predict Ovulation?

Mainstream current methods to predict the (at times) elusive fertile window can fall short for many women. From being inaccurate, too much work, or confusing to interpret, the traditional methods are widely used because they were the only tools available.

So What Makes CCBT an Improvement Over Other Methods? 

Basal body temperature (BBT), or your temperature at rest, is generally not sensitive enough to capture the subtle changes that occur prior to ovulation and is also affected by environmental factors such as medication, lack of sleep, and alcohol. Since BBT detects the rise in temperature after ovulation has occurred, the fertile window has ended. BBT also requires taking daily temperature at the same time every morning (Shilaih).

Since continuous core body temperature is collected night and day from inside the body, it is not impacted by the factors mentioned above and is able to detect temperature patterns that predict the fertile window BEFORE ovulation occurs.

Ovulation predictor kits (OPK) that measure a surge in the production of luteinizing hormone (LH) in urine are widely used, but the days with the highest probability of getting pregnant often occur before a detectable LH surge (Shilaih). The surge occurs roughly 24 hours before ovulation, which may be too late for conception (Stanford). Also, since individual LH surges are extremely variable (Direito), the LH surge can be missed, even by those who test daily (Shilaih).

CCBT measurements give women more time to have intercourse during peak fertility, maximizing the chance of conception. CCBT also avoids the limitations of LH testing with variability in the surges and duration prior to ovulation (Direito).

Peripheral sensors (those worn on the wrist, for example) may make collecting temperature easier, however, research shows that skin temperature may not be an accurate predictor of ovulation (Owen). For example, temperatures taken with a wrist temperature sensor indicated sustained 3-day temperature shift in only 82% of cycles and the lowest temperature in the cycle occurred in the fertile window 41% of the time. In addition, most temporal shifts (86%) occurred on ovulation day or later (Shilaih).

CCBT can provide accurate and precise prediction of ovulation (Aptekar), and true CCBT is collected at night and day to catch changes that may occur at any time in a 24-hour period (Shechter).

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What is Your Body Telling You?

Our bodies are really amazing. When we listen to them, they can tell us important information about our fertility and wellbeing. With Priya, you can now understand when you have the best chance of getting pregnant each cycle. 


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