What is Basal Body Temperature (BBT) and Why Track it ?
How Basal Body Temperature (BBT) works
Understanding how basal body temperature (BBT) fluctuates during the menstrual cycle provides valuable insights into ovulation. BBT is the body's temperature at rest, typically measured upon waking first thing in the morning. Reproductive hormones influence this temperature, and tracking it with precision is achieved through a basal body digital thermometer. Unlike regular household thermometers, these devices offer greater sensitivity.
What is BBT Tracking?
BBT tracking, when combined with symptom monitoring, is part of the Fertility Awareness Methods (FAM). By combining BBT changes with meticulous tracking of cervical mucus alterations, these methods estimate the most fertile days in a cycle. Recognising the highest likelihood of conception is crucial for those using FAM for family planning.
The rationale behind tracking basal body temperature lies in its subtle variations across the menstrual cycle.
During the follicular phase, BBT is slightly lower, rising post-ovulation and remaining elevated throughout the luteal phase. This temperature shift is induced by progesterone, released after ovulation to prepare the uterus for potential egg implantation. The increase is modest, ranging from 0.5ºF/0.3ºC to 1.0°F/0.6ºC, and can be influenced by external factors like illness, alcohol consumption, thyroid dysfunction and changes in sleep patterns.
Since the rise in temperature occurs after ovulation, it is important to use it with the tracking of the cervical mucus or at least have a few months of regular tracking in order to predict when the ovulation might occur. You can then validate your prediction once you notice a rise in your basal body temperature.
For accurate BBT tracking, consistency is key over several menstrual cycles. This involves measuring temperature immediately upon waking, at the same time daily, using a specialised ovulation thermometer for precise readings, and noting "unreliable" days affected by external factors. Again, environmental influences such as disrupted sleep, jet lag, alcohol consumption, illness, or medications can impact menstrual cycles.
It's essential to note that average basal body temperature varies among individuals, ranging from approximately 97°F/36.1°C to 99°F/37.2°C. This range is influenced by factors such as the time of day and activity levels.
For those monitoring BBT, it is advisable to consult a healthcare provider if there is a fever persisting beyond 48–72 hours or if there is suspicion of pregnancy. These considerations ensure the effective and informed use of BBT as a tool for understanding reproductive health.
Your can download my free BBT Tracking chart here.