Basal body temperature (BBT) is the temperature of the body when a person is completely at rest. Due to fluctuations in temperature initiated by hormonal changes during a woman’s cycle, most women use BBT to predict their most fertile days.
Introduction
When a woman ovulates, cells that made up the follicle where the egg once lived become known as the corpus luteum (yellow body, in Latin). The most important job of the corpus luteum is to produce progesterone. Since progesterone inhibits warm-sensitive neuron activity - disabling the heat-loss mechanisms, the release of this hormone results in an increase in body temperature. As a result, the body temperature of a cycling woman will rise slightly after ovulation. This increase in temperature can be measured, and after a few months, once a pattern has been established, the time of ovulation can be predicted. In case of pregnancy, the temperature will remain high. If there is no pregnancy, the temperature will drop right before menstruation.
Background
While scientifically proven, there are a few things to be considered before using BBT to understand a woman's menstrual cycle:
Type of thermometer: Since the body’s resting temperature often increases very slightly after ovulation (by around 0.5 to 1 F), a digital thermometer with two decimal places is required.
When to Temp: Since BBT refers to the resting body temperature or the lowest temperature when someone is completely still – typically after three consecutive hours of sleep, the temperature must be taken before getting out of bed. Moving around, talking or even being awake for several minutes can affect your results.
When to Chart: Charting every day, at the same time, starting on cycle day one (first day of full flow), for three menstrual cycles, is crucial to begin to see a pattern. By looking at this pattern one might be able to predict on which day a woman might ovulate - which cycle day shows a spike in temperature.
It is important to note that there are several conditions that could increase the basal body temperature, affecting the accuracy of the BBT charting. The most common are fever, lack of sleep (you need at least three consecutive hours of sleep), drinking alcohol, and stress. If any of these conditions are encountered during the BBT charting, making a note of it next to the reading can help remember why the increase in temperature.
BBT Not Just For Ovulation
While most people use BBT to understand their fertile window, charting BBT can help identify a number of complications that could be preventing a woman from getting pregnant. Practitioners of traditional Chinese medicine (TCM) may use BBT charting to determine if there is deficiency of Yin, deficiency of Yang, Blood Stagnation, Qi Stagnation, etc.
Prolonged Follicular Phase and BBT
A high BBT during the follicular phase – which indicates heat, could manifest as hyperthyroidism, weight loss, restlessness, rapid heartbeat, poor cervical mucus production, etc. Since this is an indication of heat, a prolonged follicular phase (more than 14 days) is often seen. From a TCM point of view, this is usually a Yin deficiency condition. As mentioned in previous articles, in TCM the follicular phase is considered Yin, and the luteal phase Yang. When Yin gets to its highest point it transforms into Yang (and vice versa). So, in order for the body to timely go from follicular phase to luteal phase, there has to be enough Yin in the body so that it can be transformed into Yang. If there is not enough Yin, the person will experience a longer than 14 days follicular phase and there will probably be other symptoms as described earlier.
Luteal Phase Defect and BBT
The ideal temperature during the luteal phase is between 0.5 to 1 degree (F) over the follicular phase baseline temperature. This indicates that a woman has ovulated and the corpus luteum is producing enough progesterone to create a healthy uterine lining. Progesterone levels, and consequently BBT, should remain elevated for 14 days after ovulation and drop only right before menstruation. However, a condition known as Luteal Phase Defect (LPD), characterized by low levels of progesterone, shows up on a BBT chart as low temperature in the luteal phase. If the corpus luteum is not producing enough progesterone, the uterine lining will not be properly prepared for implantation. From a TCM point of view, this could be a Yang deficiency – a lack of the warming energy. By boosting the Yang energy of the Kidney system and the Spleen system, the body can be brought back to balance.
Stress and BBT
In TCM the condition known as Liver Qi Stagnation is almost a synonym of stress. The two emotions that can disrupt the free flow of Qi of the Liver system are stress and frustration. A saw-tooth, erratic pattern in a BBT chart is a clear indication of Liver Qi Stagnation. From a more western point of view, an erratic temperature pattern on the BBT chart indicates that there is not enough hormonal regulation to normalize the cycle. Most of the time this hormonal irregularity is caused by stress. According to a paper published by the Indian Journal of Endocrinology and Metabolism:
“ Prolonged exposure to stress can lead to complete impairment of reproductive function”
One can see this pattern in a specific phase (follicular, luteal) or through the entire month. Sometimes elevated hormones like prolactin and estrogen can cause this pattern as well. Resolving Liver Qi Stagnation (acupuncture, herbs) will help the body metabolize the excess hormones.
Nutrition & Exercise and BBT
A slow step-like pattern on a BBT chart in the luteal phase is usually seen in people that don’t move much or have a poor diet. In TCM, exercise and diet are crucial to keep the Qi flowing freely. However, strong emotions can also stagnate the free flow of Qi. If a BBT chart shows this unique pattern, it would be a good opportunity to look at the amount of exercise that one might be doing and the quality of the food that one might be eating.
Conclusion
BBT, when done correctly, is a great tool to estimate the fertile window of a woman, as well as identifying other conditions that could be getting in the way of getting pregnant. A well-done BBT chart can help identify if there’s stress in the system, if the woman is suffering from Luteal Phase Defect, or even if she needs to exercise more or eat better. The best data for a good BBT chart is the temperature that is taken upon waking up after being asleep for at least 3 hours, the temperature is taken every day of the cycle at the same time, and a digital thermometer with two decimal places is used.
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