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How to Accurately Predict Ovulation & Fertility: Circadian Rhythm & Core Temperature

How to Accurately Predict Ovulation & Fertility: Circadian Rhythm & Core Temperature

Kindara | May 26, 2021 | trying to conceive
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How can circadian rhythms and core temperature predict ovulation and fertility?

For decades, basal body temperature (BBT) was the gold standard in using temperature measurements to track fertility. It’s always had its limitations, but alternative temperature tracking methods simply weren’t widely available until recently. Now, continuous core body temperature (CCBT) has emerged as a way to accurately predict ovulation and fertility (1, 2).

CCBT data can be used to identify circadian rhythm patterns and observe how they change throughout the different phases of the menstrual cycle. This is especially useful when it comes to predicting ovulation, something you can’t do with BBT tracking (2). Read on to learn what circadian rhythms have to do with fertility and why monitoring CCBT can help couples maximize their chances of getting pregnant.

What are circadian rhythms?

You’ve probably heard that circadian rhythms can influence your sleep cycle, but their job goes far beyond that. These biological rhythms include a wide range of physical, mental, and behavioral changes that happen in your body every 24 hours. (The term circadian comes from the Latin words circa, meaning “about,” and dies, meaning “day.”) Plants and animals developed these rhythms to make their bodies’ cycles match up with the 24-hour days we experience on Earth (2, 3).

Circadian rhythms are influenced by the way light changes throughout the day. This is why you may experience jet lag when traveling to different time zones and why people working the night shift may have a hard time getting quality sleep during the morning and afternoon. When your body has trouble syncing up with the 24-hour day, it may cause other complications too, such as increasing your risk of weight gain, sleep deprivation, and even some diseases (2, 4). 

Not only do circadian rhythms help control your sleep schedules — they’re the reason your body releases melatonin when it’s time for you to go to sleep — but they also have a say in almost all of your body’s functions, including your temperature, hormones, and brain function (2, 4). 

How is core temperature related to circadian rhythms? 

When you use a thermometer to measure your temperature in your ear, mouth, or on the surface of your skin, it’s called your peripheral temperature. Core body temperature, on the other hand, is your body’s internal temperature. Unlike your peripheral temperature, your core body temperature isn’t influenced by the temperature of your environment (5). 

Your body’s processes depend on your core temperature staying within a tight range, and it has safeguards in place that keep it from varying too much. This is why your body sweats when it gets too hot and creates heat (such as by shivering) when you get too cold (5, 6).

Previously, one of the only ways to study circadian rhythms was to take blood samples and monitor melatonin levels. Fortunately, core body temperature is much easier than melatonin to monitor continuously. Since CCBT typically isn’t influenced by environmental factors, it can be a good marker of your circadian rhythm patterns, including the ones related to fertility and the release of hormones (2, 7, 8).

What does your core temperature have to do with fertility?

Circadian rhythm cycles are around 24 hours, but they vary slightly with the different phases of the menstrual cycle. This phenomenon is called the circamensal rhythm. It’s layered on top of the body’s circadian rhythms, and it influences core body temperature patterns throughout the menstrual cycle (9, 10).

These core body temperature patterns can help you accurately identify the fertile window (the 5 days before ovulation and the day of ovulation) by predicting ovulation before it happens. Pinpointing and having sex during your fertile window is one of the best ways to increase your chances of conceiving each cycle (7, 8, 9, 11, 12).

One 2016 study observed this by measuring CCBT in women and tracking how their temperatures changed throughout each menstrual cycle. Lower temperatures were observed in the follicular phase of the cycle (before ovulation) with a slight dip in temperature about 2 days before ovulation. Then, higher temperatures were observed in the luteal phase (after ovulation) (13).

The temperature changes that happen before ovulation are generally too subtle to be picked up by standard oral or skin thermometers. Because CCBT measures your internal temperature, it’s able to capture these changes in time to give you a heads up before you ovulate (13). By tracking CCBT, you can plan to have sex during your peak fertility — the  2–3 days before ovulation (when the slight dip in core body temperature happens) and on the day of ovulation itself (12). 

How is continuous core body temperature different from peripheral temperature?

Measuring temperature to track fertility isn’t a new concept. Basal body temperature has been used for decades to confirm ovulation (1). And, in recent years, a growing number of fertility sensors have entered the market. CCBT differs from these options in its accuracy and its ability to predict ovulation before it happens (14). Let’s take a deeper look.

Basal body temperature

Basal body temperature (BBT) is your temperature at rest. During the beginning of your cycle, before ovulation, it stays within a certain range. After ovulation, BBT increases by about 0.5–1 degrees Fahrenheit and stays elevated until the start of your next cycle. By itself, BBT isn’t an effective way to promote pregnancy because it can only confirm ovulation after it happens. By this time, the fertile window is over, and it’s not possible to conceive until the next cycle (15).

Unlike CCBT sensors, BBT thermometers aren’t typically sensitive enough to pick up the subtle temperature changes that happen in the days before ovulation. BBT tracking has some other drawbacks as well. First, it requires sticking to a strict routine and taking your temperature at the same time each morning immediately after you wake up. Any variation in this routine could affect the accuracy of your reading (15, 16).

Second, BBT readings can also be impacted by many other factors, including illness, fever, shift work, alcohol consumption, certain medications, and even jet lag (17). CCBT, on the other hand, is measured consistently from the inside of your body. The above factors won’t impact how well CCBT measures your circadian rhythms and predicts ovulation (13).

Fertility sensors

Peripheral fertility sensors, such as those worn on the wrist, may make it easier to track your peripheral temperature, but they may not be the most accurate way to predict ovulation (18). They can show temperature patterns without the hassle of BBT tracking. However, they aren’t a reliable way to identify the slight temperature shift that happens before ovulation, which is when you have the highest chances of conceiving (16).

CCBT tracking gives you the power to track your fertility and identify your fertile window before it’s over. You simply can’t get that information using BBT thermometers or peripheral temperature sensors. By using CCBT to predict ovulation before it happens, you’ll have more time to have sex when you have the best chance of conceiving (14). 


Want to learn more about using CCBT to maximize your chances of getting pregnant? 

Check out the Priya Fertility System and take charge of your fertility today.

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Catherine Poslusny is a writer and content marketing strategist based out of Norman, Oklahoma. She's written for healthcare companies since 2016, and she's most passionate about her work in women’s health, fertility, and reproductive rights. You can find her at catherinerosewrites.com.  

References +
How Not to Waste Another Month When Trying to Conceive
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