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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. But, it was when I was struggling with what I now know was undiagnosed endometriosis. And, I learned early how bad endometriosis is on reproductive health and fertility.

Consequently, the struggles I had with inconsistencies with my basal body temperature and cervical mucus revealed how endometriosis not only causes painful periods and chronic pain. But, it contributes to other underlying issues such as ovulation dysfunction and thyroid complications. Therefore, 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. Instead, I’m strictly focusing on the link between endometriosis and its impact on basal body temperature. Furthermore, I want to share what I’ve learned about potential causes for these fluctuations in basal body temperature and how to overcome them. But for starters, let’s focus on defining basal body temperature 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 starting your day. Taking your temperature before you eat, drink, or perform 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.

fertility awareness chart with basal body temperature thermometer

Charting Basal Body Temperature

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. Therefore, you can expect an average range of temperatures to be between 97.0-97.7 pre-ovulation.

However, once there’s a surge in the luteinizing hormone, your temp may drop relatively low. Then as progesterone is secreted and ovulation occurs, your basal body temperature will rise and stay between 97.7-99.0.

Yet, 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. 


How Endometriosis Impacts Basal Body Temperature

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


Elevated Basal Body Temperature 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 cycle. But, for many with endometriosis, this temp drop doesn’t occur. Instead, you may notice that your basal body temperature remains elevated and doesn’t decline until around day three of your cycle, maybe even later. 

woman looks at basal body temperature thermometer


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 3 months, suggesting an ongoing issue. The study suggests that tracking and assessing such a metric could be another beneficial screening tool for endometriosis.


Excessively Low Basal Body Temperature Pre-Ovulation

Another common basal body temperature 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 thyroid’s ability to function effectively. Moreover, the thyroid has an important job.

woman shows a low temperature displayed on basal body temperature thermometer

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, having a hormonal imbalance can lead to excessively low basal body temperatures. 

As mentioned earlier, normal basal body temperature during the follicular phase is anywhere between 97.0-97.7 degrees Fahrenheit. Therefore, 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. The release of this hormone 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 basal body temperature. Furthermore, this increases issues with a shortened luteal phase and thin endometrium.

On average, the luteal phase lasts anywhere between eleven to seventeen days. And during this period, the egg travels down the fallopian tube and, if fertilized, implants onto the uterine wall. Therefore, experiencing a ten-day or shorter luteal phase may indicate hormonal imbalance and dysfunction. And may pose a problem when trying to conceive

woman recording her basal body temperature

Fertility Tracking: Another Important Health Metric

More research regarding basal body temperature and endometriosis should be done. The reason is that prior studies that establish basal body temperature and fertility charting as beneficial screening tools for endometriosis.

Furthermore, as it pertains to thyroid imbalance, tracking basal body temperature is recommended to manage and monitor your thyroid. Doing so will provide feedback on what’s working versus not working, especially regarding 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, some are out there that find merit in it.

Researching and choosing a doctor that recognizes and respects this method will 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?