Written by Ali Long: Ali is an intern at BNC, an undergraduate psychology student, and will be graduating in 2024! She plans to one day pursue a career as a registered dietitian where she can help women find the root cause of their hormone-related health issues. Her approach centers on utilizing nutrition as a powerful tool to alleviate physical and psychological symptoms, which is why she is specifically interested in the holistic approach to health. On her days off from school, she enjoys pilates, weightlifting, traveling, cooking, baking, and experimenting with different types of coffee!

Edited and revised by Emily Cafarella: Click here to read her bio and learn more about her!

Ever wondered about the subtle cues your body sends about its inner workings? Our bodies employ various methods to signal the balance of our hormones, and one of the ways our body does this is through our basal body temperature (BBT).

Keep reading today while we break down what BBT is and why it’s important to be tracking it for both those trying to conceive and those wanting a non-hormonal method of birth control.

What Is Your Basal Body Temperature?

So, what is our basal body temperature? Our basal body temperature refers to the lowest naturally occurring body temperature recorded after a period of rest [2].

Our BBT is an amazing tool that can help us understand our menstrual cycle and when ovulation has occurred. Please note that BBT tracking only confirms ovulation after it occurs. In other words, it does not predict ovulation.

Fertility Awareness and BBT

BBT tracking can be truly beneficial for everyone. Regardless of your goals, knowing at what point of your cycle you are at is extremely helpful for optimizing overall health!

For instance, if your goal is pregnancy, tracking your BBT can help you understand that you are ovulating and when that time frame has passed [2]. Likewise, if your goal is to avoid pregnancy, tracking your temperatures can help you understand when your fertility window is complete.

On the other hand, if you are not concerned with either, tracking your BBT can simply be beneficial in understanding what symptoms may be associated with certain periods throughout your cycle- pointing you towards determining if you have any depleted or elevated hormones!

How is BBT Measured?

Basal body temperature is measured through a basal body thermometer after a period of rest.

Typically, when measuring your basal body temperature, the best time to do this is first thing in the morning. When you are taking your temperature, make sure to leave the thermometer in place for five minutes before pushing the “on” button. Most people like to leave it on their nightstand overnight so that it is ready in the morning.

In addition, when you are tracking your BBT, especially for fertility and menstrual cycle purposes, you want to ensure that you are doing it every morning around the same time.

Note that if it is not at the same time every day, you may see varying temperatures. However, if you wake up a little earlier or later one day, don’t keep this from stopping you from tracking your temperature! Rather, make a note of it so when you are looking at your patterns in BBT, you understand why there are influxes on some days.

In addition to the standardized method of using a thermometer under the tongue, there are newer products out there, like the Oura ring and the Natural Cycles app, that can be used to make the process of tracking your temperature easier. This method for example, is a ring that just needs to be worn on your finger overnight and it will automatically track your temperature. All you have to do is open the app in the morning for the data to update!

Factors That Influence BBT

It is important to note that outside of your typical cycle fluctuations, there are some external factors that can impact BBT.

This includes:

Poor sleep
Illness
Stress
Travel
Movement (excessive or inadequate)
Alcohol
Poor nutrition

Each of these factors can delay ovulation or menstruation which may then impact temperatures. This is important to consider if you are using BBT as a cycle tracking method for fertility awareness.

This all may seem overwhelming at first. And that’s okay! If you need to take a step back and understand the basics of your cycle, consider enrolling in hormone academy!

Hormone academy is an online self-paced course that teaches you about your menstrual cycle and how to optimize hormonal balance through diet, supplementation, and lifestyle suggestions.

In Hormone Academy you will:

Gain exclusive access to video modules designed to provide you with the education you need to optimize your hormones
Receive customized care from a registered dietitian to implement a treatment plan for your unique health needs
Have access to optional monthly video calls with a registered dietitian
Gain a community of like-minded women to set you up to succeed

Once you have a foundational understanding of your cycle, this can help you learn how to cycle track in a way that benefits you and your fertility goals.

BBT Patterns Across Menstrual Cycle Phases

At this point, you may be wondering how to know what temperatures are normal at different phases in your cycle.

For starters, there are four phases in your menstrual cycle.

Menstruation
Follicular
Ovulation
Luteal

The biggest shift you should see in your temperature is after ovulation and at the beginning of menstruation. This is mainly due to the primary hormones during each stage.

Let’s start with menstruation! Menstruation begins when you first bleed. During this phase, your hormones drop to their lowest.

As a result, your temperature will drop. At this point in your cycle, it is a great time to start tracking your temperature if you want to begin cycle tracking. This is considering that it provides your lowest temperature.

Once you hit your follicular phase, your BBT should stay relatively low until after ovulation occurs.

Ovulation is a fundamental point in the menstruation cycle because it is the main event that occurs. During ovulation, your temperature should stay relatively the same as during the follicular phase.

However, you should see a shift in your temperatures right after you finish ovulating because of the increase in progesterone that is dominant during the luteal phase.

Indicators that you have ovulated:

Three consecutive days of increased BBT have occurred.
Body temperature rises 0.5-1.0 degrees after ovulation and persists for two weeks.

The luteal phase occurs directly after ovulation. During the luteal phase, your temperature should consistently stay elevated within this range until menstruation begins and your temperature drops again. The luteal phase typically lasts for a maximum of 16 days.

NOTE: If you notice that your temperature has continued to remain elevated past 18 days, this may be a sign of pregnancy! This being said, cycle tracking using your BBT may be a good idea during the first trimester of pregnancy because a drop in your temperature can signify progesterone dropping.

This is important because one of the main indicators of miscarriages during the first trimester is low progesterone.

If you are noticing that your temperatures are off during a certain phase, this may indicate bigger issues with hormonal levels.

In this case, it is important to consult your primary health care provider or a registered dietitian that can help you understand the root cause of these symptoms.

Nutritional Changes for Optimal Fertility

If you notice that your basal body temperatures are off, poor nutrition may be one reason for this. This is because the food you eat can change how your body produces and releases hormones [1].

If you believe this may be the case for you, try to focus on building a nutrient-dense and balanced diet to support optimal hormonal health!

For specific foods for fertility health, download this foods for fertility guide here!

Understanding how to take care of your body may be the first step in balancing your hormones. If you want additional guidance on supporting you in your health journey for optimal fertility, consult a registered dietitian.

Meeting 1:1 with a registered dietitian can support you and your health and fertility goals. Schedule your first free consultation here!

In functional nutrition coaching with a registered dietitian, you will receive:

A personalized approach rooted from functional and integrative background
Treatment for conditions such as PCOS, digestion issues, preconception, infertility, endometriosis, hormone imbalance, thyroid disorder and more using a holistic perspective
An assessment, evaluation, and personalized plan to heal and restore your energy while eliminating symptoms

Summary

Basal body temperature is an insightful way to track your menstrual cycle. Our bodies are amazing as they provide signals to us that it may be lacking in certain areas.

Temperature signals are one way our body does this, so it only makes sense to utilize them! The first step is to get started. Try cycle tracking on the first day of your upcoming menstrual cycle and see how it goes that cycle.

If you need guidance, don’t be afraid to reach out for support! Remember that the resources provided in this blog are always an option. It may take some getting used to, but the benefits of understanding your body are worth it!

References:

Marks V. (1985). How our food affects our hormones. Clinical biochemistry, 18(3), 149–153. https://doi.org/10.1016/s0009-9120(85)80099-0

Steward, K., & Raja, A. (2023). Physiology, Ovulation And Basal Body Temperature. In StatPearls. StatPearls Publishing.

Understanding Your Body: Decoding Basal Body Temperatures