Basal body temperature (BBT) charting serves many purposes, the most basic of which is to distinguish fertile times in a woman’s 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.
Essentially, BBT charting is used to evaluate overall reproductive health, and identify weaknesses in the menstrual cycle.
Simple BBT charting involves taking your waking (basal) temperature daily, recording it, and charting the results to track the timing of ovulation (or lack thereof), the length of your follicular and luteal phases, as well as the stability of each phase. Tracking reproductive signs, such as the presence and quality of cervical fluids, will further enhance your BBT chart analysis, telling you even more about your reproductive health and constitution.
Your basal body temperature is your body’s resting temperature upon waking. Basal body temperature should be taken with a minimum of three to four hours of relatively uninterrupted sleep, and immediately upon waking. This means you should not have gotten out of bed within the last three to four hours before taking your temperature. To get the most accurate reading, I recommend setting an alarm to take your temperature at the same time every morning, and keep your thermometer next to your bed.
I will say that BBT charting is not for everyone, and if it is not for you, please don’t feel discouraged – ovulation predictor kits can still be used to predict ovulation, and monitoring reproductive signs throughout your menstrual cycle is also helpful. Even without BBT charting, it is possible to identify times during your cycle that could use improvement. Reproductive signs such as the amount, quality, and timing of cervical fluid; mid-cycle ovarian pain; PMS symptoms, such as breast tenderness or cramping; and the length and quality of your menses – all of these reproductive signs can tell you a lot about your constitution and how best to approach optimizing your fertility.
To begin BBT charting, you will need a special thermometer intended for BBT charting. A BBT thermometer is calibrated to register lower temperatures associated with hormone levels, and will record temperatures within two decimal places (for example, 97.45°F). You should be able to find a BBT thermometer (ideally, digital) in the family planning section of most drugstores, or order online.
Basal body temperature readings are graphed for analysis reflecting weaknesses and improvements in your reproductive health over time. Day-1 of the graph represents a new menstrual cycle indicated by the first day of a full menstrual flow (not spotting). Please note that if your full flow begins in the late hours of an evening, day-1 should be recorded as the next day.
By charting consecutive menstrual cycles, patterns in your reproductive health can be discerned. Your BBT chart will also monitor the effects of chosen treatments clarifying the most beneficial types of treatment for you.
There are many factors that affect our reproductive hormones – most notably stress …and who of us does not experience significant bouts of stress? Interrupted sleep affects the pituitary gland, which regulates reproductive hormones and influences their release – do you get eight solid hours of good quality sleep every single night? (I sure don’t.) Lifestyle choices (e.g., diet, exercise, coffee/alcohol consumption) also strongly influence reproductive health. Your BBT charts will change in correspondence to lifestyle changes, and clarify whether current choices enhance, or weaken, your reproductive health.
Know that there is no perfect BBT chart. We all have reproductive strengths and weaknesses as will be evidenced in BBT charting. In terms of menstrual cycles, what is normal for many women falls outside the textbook definition of “normal,” which is a 28-day cycle with ovulation occurring on day-14. What is your “normal?” Start by clarifying this through BBT charting.
For reference, an optimal BBT chart ranges from 97.2°F to 97.8°F during the follicular phase (Phase I), and after ovulation, from 97.8°F to 98.6°F during the luteal phase (Phase II), with temperatures remaining elevated until a day or two before your period begins.
During Phase I, the ovaries produce estrogen, which results in lower basal body temperature readings. Estrogen production also generates cervical mucus, which commences up to five days before ovulation. Cervical mucus has several phases indicated by changes in consistency with the most fertile type being the stretchy, egg white-like mucus at ovulation. Phase I ideally lasts until around day-14 of a cycle and ends with a slight dip in temperature, signifying transition to Phase II.
Ovulation is the transition from Phase I to Phase II. This transition starts with a surge of luteinizing hormone (LH), as evidenced by a slight dip in temperature, up to 0.3°. This dip is then followed by a spike in temperature, about 0.5°F or higher, confirming ovulation has occurred.
Phase II, the luteal phase of the cycle, begins after ovulation has occurred. It is dominated by progesterone, a thermogenic hormone produced by the corpus luteum (a temporary endocrine structure formed from the ovarian follicle that released an egg), hence the higher temperature readings post-ovulation. After ovulation, your temperature should rise quickly, ideally over one to two days, and remain steadily elevated until just before your period. A dip in temperature begins as the corpus luteum dissolves and progesterone production ceases. This withdrawal of progesterone is what brings on menstruation. Phase II should last about 14 days if pregnancy did not occur.
On average, the total menstrual cycle lasts between 27 to 30 days, with the first day of full menstrual bleeding signifying a new cycle. The most fertile time is immediately prior to and during ovulation. Timing intercourse between 24-hours prior to, and immediately after ovulation, is important. The cervical fluid that is generated before ovulation provides a hospitable environment for sperm to live in for a few days. This allows time for sperm to make it through the uterus and fallopian tubes, and wait for the timely release of an egg.
To note: some may have a 27 to 30 day menstrual cycle and think everything is fine until they start BBT charting. Some discover they are ovulating on day-18 or 20, with a short luteal phase; less commonly, some find they are ovulating on day-11 or 12, with a long luteal phase – neither pattern is optimal. The length of their cycle may look normal, but these phase discrepancies indicate weaknesses in the reproductive cycle. Others may have relatively short or extensively long cycles, indicating insufficiencies or “stagnations.” And others still, may have irregular cycles (cycles that vary in length from month-to-month), which alone present fertility challenges around the timing of ovulation and intentions to conceive.
This is not a comprehensive list, but in the above cases, some of the underlying issues may be a difficulty in properly maturing eggs, forming a functional corpus luteum, or building an adequate endometrium for embryo implantation.
BBT charting can be a helpful tool in both conceiving and preparing your body for a healthy pregnancy. Tracking your basal body temperature and other reproductive signs is instrumental in identifying the strengths and weaknesses in your cycle.
In Part II of this article, I will discuss BBT chart analysis of the follicular phase in more depth; and in Part III, I will discuss the luteal phase. We will look at the patterns that are commonly seen in BBT charts, and what these patterns signify from a traditional Chinese medicine perspective.
I hope you have found this series of articles on basal body temperature and chart analysis helpful.
If you are interested in learning more, you may be interested in my FREE online course on BBT charting. Learn more HERE.
Dr. Jules Bogdanski, DAOM L.Ac.