Basal Body Temperature Charting (Episode 448)

Full Transcript: Episode 448

Lisa: Welcome to the Fertility Friday Podcast, your source for information about the Fertility Awareness Method and all things fertility. I’m your host, Lisa Hendrickson-Jack. I’m the author of The Fifth Vital Sign and the Fertility Awareness Mastery Charting Workbook. I’m a certified fertility awareness educator and holistic reproductive health practitioner with over 20 years of experience teaching women to connect to their fifth vital sign through menstrual cycle charting, balancing hormone health, and optimizing the menstrual cycle without hormones.

I have been consistently outspoken about hormonal birth control over the past two decades and its impact on fertility and overall health because you have the right to know how your body works and how artificial hormones disrupt that natural process. I teach women’s health professionals how to utilize the menstrual cycle as a vital sign in their practices, and I host live coaching programs to help you achieve optimal fertility and health because it’s important to have healthy menstrual cycles regardless of whether or not you want to have babies.

I’m also a wife and mother of two beautiful boys and a brand new baby girl. This podcast is designed to empower you to take full control of your cycles, your fertility, and your overall health. I’m so excited that you’re here with me today.

Today I’ll be doing a BBT throwdown. BBT stands for basal body temperature. From here on in, I’ll be saying BBT. I’ll be going through some of the most common questions that I receive about it and about wearable devices.

BBT is an interesting topic in the fertility awareness world because most women are familiar with the sympto-thermal method. The majority of my clients and practitioners tend toward the sympto-thermal method, which combines cervical mucus charting, BBT, and other signs including cervical position and secondary signs.

However, there are methods that are used without BBT. There are practitioners who discourage its use, so it’s helpful to understand why.

One reason some practitioners avoid BBT is because it’s variable. It changes and fluctuates based on a variety of factors happening in your life. I would argue that this variability is one of the reasons BBT is helpful, especially when you’re looking at the menstrual cycle as a vital sign.

For practitioners, BBT analysis provides an additional measure of metabolism. It can guide conversations about adequate food intake, protein, overall calories, activity level, and hormonal balance. It can also help identify potential underlying issues like thyroid dysfunction. It may reflect sleep patterns, stress levels, allergies, or immune triggers.

From a charting perspective, temperature is also helpful to confirm ovulation. There are many useful applications for it. I’m in favor of using it, but it’s important to know there are methods that do not use it.

With mucus-only methods, ovulation can be accurately confirmed without temperature. I prefer to have the secondary sign of BBT as a cross-check, but there are women who confidently confirm ovulation using mucus alone.

One of the most frequent questions I receive is: What kind of thermometer should I use?

You don’t need a fancy or expensive thermometer to get an accurate temperature. A $15–$20 thermometer works just fine. The basic requirement is that it measures to at least one decimal point. Most measure to two decimal points, which is sufficient.

Additional features like memory recall, backlight, or switching between Celsius and Fahrenheit can be helpful. There are also wearable devices that track temperature overnight and sync to an app, so manual entry isn’t required. The final decision depends on your preferences and circumstances.

Another common question is: What is a normal pre-ovulatory temperature?

I specify pre-ovulatory because temperatures differ before and after ovulation. Excluding period temperatures, which can fluctuate, pre-ovulatory temperatures should ideally be above about 97.4°F (36.3°C).

There is a normal range for human body temperature. If your temperatures are consistently below range, that can signal something worth investigating.

In my charting workbook, the Fahrenheit chart cuts off at 97.0°F and the Celsius chart at 36.0°C. If temperatures fall below that, they’re off the chart. That cutoff is intentional. It indicates something may be going on.

One common issue is not taking temperature correctly. I recommend holding the thermometer in place for a full 10 minutes before turning it on. This allows it to warm up and stabilize. Many women see their temperatures normalize just by following this rule.

If you’re already doing that and temperatures are still low, it can reflect factors such as insufficient calorie intake, thyroid concerns, nutrient deficiencies, or inadequate sleep.

Post-ovulatory temperatures should be higher than pre-ovulatory ones. In Fahrenheit, that may mean 97.8°F and above, with at least a few temperatures over 98.0°F. In Celsius, you’d expect 36.6–36.7°C and sometimes one reaching 37.0°C.

These are general guidelines. Individual charts vary and require personalized interpretation.

Another question is: Does BBT predict ovulation?

No. BBT confirms ovulation.

Before ovulation, estrogen predominates as the follicle develops. After ovulation, progesterone rises. Progesterone has a thermogenic effect—it raises body temperature.

You ovulate first, then progesterone rises, and that rise increases temperature. That is what BBT measures.

If you haven’t ovulated, you won’t see a sustained temperature shift. After ovulation, you should see two distinct groups of temperatures: lower pre-ovulatory and higher post-ovulatory. You should be able to draw a line between them.

BBT confirms ovulation and should correlate with a shift in cervical mucus.

To confirm ovulation, we look for three temperatures higher than the previous six. These must be undisturbed readings.

You should also see a corresponding shift in cervical mucus. After ovulation, progesterone reduces mucus production. Typically, mucus dries up.

What if temperatures are erratic?

First, implement the 10-minute rule. Many erratic charts stabilize once technique improves.

You will almost always have at least one unusual temperature per cycle. The goal isn’t perfection. It’s identifying consistent patterns.

If fluctuations persist, consider factors like sleep duration, wake time, alcohol, illness, allergies, or travel. Track these variables. Most apps allow you to log wake time and disturbances. Often there’s a simple explanation.

If your temperature rises and then falls, return to the confirmation rules. You need three sustained temperatures higher than the previous six. If temperatures repeatedly drop below the coverline, ovulation likely has not occurred yet.

No sustained rise means no confirmed progesterone rise. Without progesterone, you won’t see a stable post-ovulatory pattern.

If wake times vary, you don’t need to force a rigid schedule. Record wake time and hours slept so patterns can be interpreted accurately.

Shift work can complicate interpretation, but sometimes it’s less problematic than expected. Try charting consistently and recording disturbances before assuming it won’t work. If needed, a wearable device may offer additional stability.

Postpartum, temperature is less useful before ovulation resumes. Mucus-only charting may be more appropriate during that stage. Once cycles return, temperature can be reintroduced.

Regarding wearables, traditional BBT reflects resting metabolism after at least five hours of uninterrupted sleep. Some wearable devices measure temperature throughout the night and provide an average sleep temperature. That is not identical to classic BBT.

The benefit of wearables is stability and convenience. Many women find confirming ovulation easier with them.

A limitation is that average sleep temperature may not provide the same metabolic insight as a true basal reading. Some individuals use both a wearable and an oral thermometer for deeper interpretation.

The three classic BBT sites are oral, axillary, and vaginal. Devices worn on the wrist or finger measure peripheral temperature, which may run lower.

The purpose of wearables is to confirm the shift between pre- and post-ovulatory phases. They are not designed to diagnose metabolic concerns.

Regardless of device, learn a specific method and use mucus as a cross-check. Technology supports fertility awareness, but it does not replace understanding the method.

Different thermometers can yield slightly different readings. If temperatures appear consistently too high or too low, rule out device error.

To recap, BBT has two primary applications: confirming ovulation and offering potential diagnostic insight. Not all methods use BBT, and there are reasons for that. With proper interpretation, fluctuations can be understood.

We covered thermometer selection, normal temperature ranges, confirming ovulation, erratic temperatures, rises and falls, inconsistent wake times, postpartum charting, and wearable devices.

BBT interpretation isn’t always straightforward. Many variables influence temperature patterns. With consistent tracking and education, meaningful patterns can be identified.

Until next time, be well and happy charting.