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I officially started tracking my basal body temperature over two years ago. My reasons focused primarily on getting confirmation that something was up with my fertility. It was during a time when I was struggling with what I now know was undiagnosed endometriosis. And, I learned early how destructive endometriosis is on reproductive health and fertility. Consequently, the struggles I had with inconsistencies with my BBT and cervical mucus revealed how endometriosis not only causes painful periods and chronic pain. But, it contributes to other underlying issues in the form of ovulation dysfunction and thyroid complications. That’s why the fertility awareness method is super helpful for women with endometriosis. It provides so much valuable feedback and data that can fuel better decisions regarding your health. 


Why Basal Body Temperature Is Important

For brevity, I won’t be going into depth regarding the fertility awareness method. I’m strictly focusing on the link between endometriosis and its impact on BBT. Furthermore, I want to share what I’ve learned about potential causes for these fluctuations with BBT as well as how to overcome them. But for starters, let’s focus on defining what basal body temperature is and why it’s essential. 


What’s Basal Body Temperature?

Your basal body temperature represents the body’s temperature when you’re asleep and at rest. When following the fertility awareness method, you’ll take your temperature first thing upon waking. And it can be measured orally, vaginally, or anally. Additionally, you’ll want to make sure you’re taking your temperature before you start your day. Taking your temperature before you eat, drink, or perform any of your daily morning activities prevents inaccuracy with readings. Furthermore, basal body temperature can help identify when you’re fertile, which aids in conception or avoiding pregnancy. It’s also helpful for learning more about your fertility and health.


Charting BBT

As it pertains to charting basal body temperature is used to track temperature changes throughout your cycle. Usually, you’ll experience a low basal body temperature during the follicular phase. You can expect an average range of temperatures to be between 97.0-97.7 pre-ovulation. Once there’s a surge in the luteinizing hormone, your temp may drop quite low. Then as progesterone is secreted and ovulation occurs, your BBT will rise and stay between 97.7-99.0. Yet, with endometriosis estrogen dominance, chronic inflammation, and co-morbidities can cause basal body temperature to be lower in the follicular phase. Furthermore, it can contribute to the slow decline of temperature during the first three days of menstruation. 

basal body temperature

How Endometriosis Impacts Basal Body Temperature

Endometriosis is commonly associated with estrogen dominance. Which, as the name suggests, describes a hormonal imbalance in which estrogen levels are higher than progesterone levels. Furthermore, endometriosis is also known for being inflammatory. Consequently, the combination of high estrogen and chronic inflammation causes dysfunction with basal body temperature and reproductive health.


Elevated BBT During Menstruation

When tracking your fertility, you’ll notice how there’s typically a bi-phasic difference between your pre-ovulation and post-ovulation temperatures. This has everything to do with the secretion of hormones during your menstrual cycle. Furthermore, a decline in temperature post-ovulation signifies the onset of menstruation and a new period. But, for many with endometriosis, this temp drop doesn’t occur. Instead, you may notice that your BBT remains elevated and doesn’t decline until around day 3 of your cycle, maybe even later. 


A study conducted in 1990 on 18 infertile women with diagnosed endometriosis revealed that two-thirds of the women evaluated experienced a slow decline in basal body temperature during days 1-3 of menstruation. Furthermore, this decline was observed over a 3-month period, which suggests that it’s an ongoing issue. The study goes on to suggest that tracking and assessing such a metric could be another beneficial screening tool for endometriosis.


Excessively Low BBT Pre-Ovulation

Another common BBT abnormality is experiencing lower than average body temp readings. And, while you’re supposed to have low temps during your follicular phase experiencing extremely low temps is often associated with hormonal imbalance and thyroid dysfunction. Additionally, thyroid complications are associated with endometriosis. Furthermore, having higher than average estrogen levels impair the thyroids ability to function effectively. Moreover, the thyroid has an important job. It’s responsible for regulating many systems and functions within the body, such as digestive function, brain development, bone maintenance, and basal metabolic rate. Hence why having a hormonal imbalance can lead to excessively low basal body temperatures. 

As mentioned earlier, normal BBT during the follicular phase is anywhere between 97.0-97.7 degrees Fahrenheit. Having temps that fall below this range may indicate a hormonal imbalance or thyroid complications in the form of hypothyroidism. If this is something you’re noticing when tracking your fertility, it’s time to discuss your concerns with your doctor. Perhaps look into having your thyroid levels checked and have a full hormone panel done. 


Luteal Phase Defect

Lastly, experiencing issues with a luteal phase defect may also contribute to dips in your basal body temperature post ovulation. The luteal phase is responsible for preparing the body for a potential pregnancy. It does so once an egg is released, and the corpus luteum secretes progesterone, which supports the health of the endometrium and enables implantation. Having inadequate levels of progesterone can interfere with this process.

 As discussed prior, endometriosis contributes to progesterone insufficiency. The inability of the body to secrete adequate amounts of progesterone during the luteal phase can add to fluctuations in BBT. Furthermore, this increases issues with a shortened luteal phase and thin endometrium. On average, the luteal phase lasts anywhere between 11 to 17 days. And, during this period the egg travels down the fallopian tube and if fertilized implants onto the uterine wall. Experiencing a 10-day or shorter luteal phase may indicate hormonal imbalance and dysfunction. And, may pose a problem when trying to conceive

basal body temperature

Fertility Tracking: Another Important Health Metric

In my opinion, more research regarding basal body temperature and endometriosis should be done. Especially in light of prior studies that establish basal body temperature and fertility charting as a beneficial screening tool for endometriosis. Furthermore, as it pertains to thyroid imbalance tracking, BBT is recommended as a means of managing and monitoring your thyroid since it provides feedback on what’s working versus what’s not working especially, as it pertains to medications and lifestyle modifications. 

Additionally, fertility tracking establishes a tangible history of your health and provides black and white evidence of what’s happening within your body. And, while it’s unfortunate that many doctors fail to take this health metric seriously, there are some out there that find merit with it. Researching and choosing a doctor that recognizes and respects this method is going to be necessary, especially if you’re on a diagnostic journey to determine underlying issues contributing to health complications such as infertility, painful periods, cyclical pelvic pain, etc. Seeking the help of reproductive endocrinologists, fertility specialists, and naturopaths may prove an excellent place to start.



  1. The American Fertility Society | Fertility and Sterility Vol. 54 No. 6 December 1990 | Sungji Chai, B.S., Robert A. Wild, M.D. 
  2. Fairhaven Health | Charting Basal Body Temperature Information and FAQ 
  3. Boost Thyroid | Basal Body Temperature and Thyroid Function
  4. Early Pregnancy Tests | What Is A Luteal Phase Defect?



About the Author 

women's health and wellness blogger

Hi, my name is Kathleen but you can call me Kat. I’m a health and wellness professional turned freelance writer and content creator.  You can find me on  YouTube and Instagram. If you take the opportunity to visit me on my other platforms don’t hesitate to leave a message, I would love to hear from you!



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