top of page

What I didn't know about Basal body Temperature but wish I did.

Everything I learned about Basal Body Temperature that helped me understand my body better.

When I first started learning about Fertility Awareness-Based Methods, I understood that you are supposed to track your BBT but I honestly wasn't really sure of how that had anything to do with my menstrual cycle or why it was such an important piece of my fertility puzzle.

If you are like me and you are not really sure why your BBT matters, don't worry, you are far from alone. A lot of women are still in the dark about this plus there are a lot of research out there that states conflicting information about it stating that it can't really be used as a way to confirm ovulation.

Yes, your BBT is a 'test and tried' by many women in the world who use FAM as their preferred birth control method that can tell if you have ovulated or not in a cycle.

So let's take a step back to understand what is your BBT in the first place, and why it is such a cool tool for you to understand your body better. BBT or Basal body temperature is your temperature when you're fully at rest. It's usually taken first thing in the morning before you do anything , before you even roll out of bed, or stand up and go to the bathroom. Ideally this temperature is taken every day around the same time and after 3 hours of uninterrupted sleep. I can see you Mamas rolling your tired eyes as you read this...

If that's you, read on!


Why Is BBT so important to track?

If you are interested in using FABM as your birth control method, understanding and tracking your BBT is super important as it's one of the key indicators that you have in fact ovulated. However, its also an incredible tool to use if you are experiencing hormonal imbalances or going through perimenopause.

Basal body temperature (BBT) charting serves many purposes, the most basic of which is to distinguish fertile times in your menstrual cycle and confirm if ovulation has occurred. If you are planning to conceive, BBT charting is also an incredibly useful tool in identifying potential fertility challenges, and optimizing your reproductive health in preparation for pregnancy.

However BBT charting can also be used to evaluate overall reproductive health, and identify weaknesses in the menstrual cycle. 

Ovulation may cause a slight increase in basal body temperature. Why? Because progesterone, one of your reproductive hormones have a measurable impact on your temperature. Progesterone prepares the uterus for the implantation of a fertilized egg. I like to think of estrogen as the contractor that's building your house and progesterone as the people who get hired to clean everything, put all the furniture in, and make the place ready for you to move in. :)

BBT is slightly lower in the follicular phase (the first half of the menstrual cycle), and rises after ovulation and stays high throughout the luteal phase (the second half of the menstrual cycle). The temperature change after ovulation is slight — BBT rises by only about 0.5ºF/0.3ºC to 1.0°F/0.6ºC — and may be easily affected by factors such as illness, alcohol, having had a late night or disturbed night, oversleeping, holidays, travel, time zones, shift work, stress, gynecologic disorders, and medications (Clubb & Knight, 1999).

What I learned when I started tracking is that every cycle is a bit different but you can always recognize a pattern in your temperatures or you can recognize a lack of a pattern which could indicate that something is off with your hormones or health.

How do I track my temperature?

There are a few ways to track. Getting a BBT thermometer is in my opinion the most accessible and one of the least high tech ways to do it. It's more sensitive than a regular household thermometer, and it measures temperature more precisely, meaning you get a reading of 2 decimals (like 36.54 instead of 36.5 Celsius). A basal thermometer shows you the temperature in tenths of a degree. This allows you to note tiny changes in body heat.

I tried the thermometer thing at first, however having a child who would always wake up during the night made it really hard for me to keep track of the readings. There are loads of fertility or menstrual cycle tracking apps that allow you to sync your readings automatically, which makes the process easier.

I had to go high tech though and I discovered Tempdrop. It's an arm thermometer and it measures your temperature throughout the night and it basically gives you an average the next morning. This means that this is NOT your real BBT, but it can be used to see the same patterns and changes with your hormonal fluctuations.

Plus it's pretty easy to uploads the temps to the app and you can see your chart pretty easily and also make notes in case you got a fever one day and need to cancel a temperature out of your chart. Pretty cool, right?

How do I find out if my menstrual cycle is healthy?

What I didn't know after tracking for a while was that my below average temperatures were signaling a sluggish Thyroid! It might not be the case for everyone, but it's worth looking into and getting tested if your temperatures are below average as well as too high. When we have a healthy thyroid and metabolism we will have temperatures above 36.0C. Other symptoms of hypothyroidism: hair loss, cold hands, and feet, low energy, low mood, constipation, or irregular bowel movements. 

If you notice any of the imbalances above, you can take your charting information along with your symptoms to your health care practitioner for further diagnosis and testing.

You can learn so much about your menstrual cycle when you start tracking your BBT! I learned that before ovulation, my temperature usually drops slightly and then starts to rise.

That does not mean that you can use your previous cycle charts to predict ovulation though. Your BBT will only CONFIRM ovulation! We need to move away from the notion that we are like machines and ovulate every month on the very same day (maybe you do, but for the most of us, it differs every cycle) and understand that as women we are influenced by many things like stress levels that may signal our bodies that it is not safe to ovulate which can delay that day or even not happen that cycle.

Another example that I found fascinating about tracking your BBT was that if your luteal phase temps rise slowly and stay low, it could mean you have low progesterone. On the other hand, if your temps stay in the same follicular range for the entirety of your cycle, that is an indication that you are not ovulating and may be experiencing an anovulatory cycle.

Your BBT can help you predict our period! Your temperature can dip back down to lower Follicular phase temps 0-3 days prior to menstruation. The first day you see temps start to go down in your Luteal phase, you can be prepared for menstruation to start ,and not be caught off guard! UHU!

Your period will usually arrive 10-14 days after our temp shifts upwards following Ovulation so you will know when to expect your next period after you confirm your temp shift. 

What about tracking during Perimenopause?

I really recommend charting until you reach menopause because it will make the natural ebb and flow of the hormones more understandable. When you chart your cycle with Fertility Awareness-Based Methods, you will see changes to your cycle during perimenopause just as you may have seen changes due to your thyroid condition, poor diet, lack of exercise, a hormone imbalance, stress and sometimes even a disease because all these things could also cause hormones to go out of whack...

If you are tracking your cervical mucus for example, you are looking at a symptom of the hormone estrogen. If you are tracking your BBT, you are observing a symptom of progesterone rising. I think it's so much easier to navigate this journey once you know what is going on with your hormones, it might even give you a sense of peace, once you know what is going on with you.

I hope this blog has given you loads of reasons to dive deeper into the understanding of your amazing female body and if you want to learn more about your menstrual cycle, I have a FREE workshop on The 4 Phases of the Menstrual cycle here.

Body literacy may be the most powerful thing you do for you and for the next generations of women to come.

With love.


bottom of page