How and Why to do a BBT Chart

A Basal Body Temperature (BBT) chart is a great resource to gather information about a woman’s menstrual cycle, fertility, and to track when ovulation occurs.  When patients come in with fertility challenges, I typically ask them to “begin charting.”  Keeping track of their daily temperatures, mucus patterns, other bodily changes, intercourse and menstruation gives me a plethora of useful information.

While it is not helpful to identify ovulation before it occurs, it confirms it after the fact. Looking at a woman’s chart for a few months helps to identify patterns that can influence ovulation and fertility. It also confirms pregnancy.

Women can also use this data as a form on natural birth control, but only with clear understanding, experience and regular cycles! In fact, my husband and I have used this method of “natural family planning” for over 18 years and have only been pregnant when we tried. Again, my cycles are regular and I have studied this extensively. It is only recommended in monogamous relationships in which both partners have been tested for STD’s since there is no protection from them using this method.

A few things to know before you begin:

• The chart begins on the first day of your period.
• It is best to take BBT at the same time everyday, give or take 20 minutes.
• Because it is the body’s resting and lowest temperature, the best time to take BBT is upon waking, before you even put your feet on the floor or use the bathroom.
• Keep the chart, a pen (or app) and your thermometer right next to your bed for ease.
• After marking the date, time and temperature, it is good to move to the bathroom to evaluate your cervical mucous.
• Note: if you have a restless night or get out of bed up to 4 hours before waking and move around, it can throw off your BBT. Alcohol can also influence your BBT. It’s good to add journal notes each day so you can recognize outliers in the chart.
• Also use the chart to note other physical changes you notice throughout the month, such as ovulatory pain, breast changes, emotions etc…
• Collecting and charting BBT data can create a lovely morning ritual that allows you to get to know your cycle, help create regularity in your wake times, and to create intention around conception.

Cervical Mucous

Cervical mucus is a fantastic indicator of fertility. Watching changes in your mucus throughout the month is another piece of useful information that can be used in conjunction with charting your temperature to indicate ovulation. Use the chart to note specific descriptions of the consistency of the mucus.

Right before ovulation, cervical mucous will become slippery and have the look and feel of egg whites.  This type of cervical fluid is conducive for sperm to survive and reach the egg for fertilization. When progesterone levels are high, cervical mucous tends to be more opaque, dry, or have a paste quality. This happens right before and after menses.

Hormones, Ovulation and Menstruation

There are 4 hormones at work in your monthly ovarian cycle. Estrogen, Progesterone, Follicle Stimulating Hormone (FSH), and Luteinizing Hormone (LH).  After menses, FSH begins to climb to help grow follicles on the surface of the ovaries to prepare to release an egg. LH levels are low and steady in the first half of your cycle and support the growth of follicles on the ovary until mid-cycle, when LH surges to encourage one mature follicle to burst and release an egg. This is the exact moment that ovulation has occurred.

LH then drops as it helps with clean up and repair of the follicle in preparation for the next cycle.  This process also signals the body to increase progesterone in weeks 3 and 4 of the cycle, an essential hormone in the early stages of pregnancy if fertilization occurs. During weeks 1 & 2 of your cycle, estrogen slowly climbs, and peaks at ovulation while progesterone slowly climbs and peaks around when fertilization would take place, a little after ovulation or it tapers off with menstruation.

How does the Ovarian Cycle Relate to my BBT Chart?

Creating a BBT chart allows you to find a pattern in your unique cycle to help plan intercourse for optimal pregnancy outcome.  As a practitioner, the chart helps to inform my treatments, herbal protocols and other supportive measures to balance hormones. If you notice a slight drop in BBT on one day, before a spike the following day of your cycle, then this is likely the day you can plan for intercourse. In a “regular cycle”, you will notice a relatively even pattern of BBT numbers for the first half of your cycle, then a dip, followed by a spike in BBT that lasts until menstruation.

In the event that you become pregnant, your BBT will remain higher than average for the duration of the cycle.  Most of the BBT charts and ovulation trackers are designed for a 28-day cycle, but a woman’s cycle is as unique as each of us, and it’s important to see what your individual body is doing.  Some women ovulate on day 12, while others may ovulate later in their cycle.

There are a lot of printable templates online that can be used for BBT charting, and interactive apps that you can download on your phone. The most important thing to remember is to be consistent in order to get the best data.  The thermometer you use should measure to the tenth.

Doing this type of charting can be a beautiful way to collect information about your body as you plan for pregnancy, or wish to avoid it.  It creates a morning ritual that allows space to visualize what is happening in your body on each day of your cycle.  It also brings profound intention to conception and pregnancy and can help identify if there are any irregularities that can be examined further.

References

Bull, J. R., Rowland, S. P., Scherwitzl, E. B., Scherwitzl, R., Danielsson, K. G., & Harper, J. (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. NPJ digital medicine, 2, 83. doi:10.1038/s41746-019-0152-7