A basal body temperature (BBT) chart is quite simply a graph showing your basal body temperature (your temperature at the very moment you wake up in the morning after at least 4 hours of sleep) throughout the month.  It shows slight differences in a temperature and as such gives a snapshot of menstrual hormonal health.

It is done for a variety of reasons.  It is just one aspect of the Fertility Awareness Method (FAM), and can be used to avoid pregnancy or to enhance chances of conception.  The idea is that if one knows their fertile window, they can optimize it and/ or keep sperm away during that time, depending on what your goals are at this time in your life.  In my practice I consult my patients’ BBT charts for the purposes of enhancing fertility, and this is where I get the most questions.  This blog post will be most helpful to those of you trying to conceive.

It can come as a shock after years of scrupulously avoiding pregnancy to discover that it does not happen as easily as one might have been led to think in high school.  (Although to be fair, the youthfulness of high school bodies may make conception a lot easier, so good that you were so careful.). After a few months of failed attempts, couples often begin to wonder if they should take a closer look at what they are doing.  Conception in the best of situations can take many months; it is good to shift lifestyle habits towards optimal health and begin gentle investigation early while also resting in the knowledge that bodies and nature do things in their own time.  There is a delicate balance to be struck between optimizing your odds and being relaxed.  

A BBT chart can confirm something very important — whether or not the ovaries are ovulating.  The only other way to know this is by carefully tracking with imaging what the ovaries are up to throughout the cycle.  “But wait!” You say, “my OPK strips tell me that I am ovulating!”  Actually, they measure your luteinizing hormone (LH).  This is your body’s messenger that tells the growing egg it is time to pop out of the ovary.  Your body can send this message, but the ovaries do not always respond.  A BBT chart is a great way to see if the eggs are leaving the ovary, and also to give a general picture of hormonal health.

BBT charts, like egg white cervical mucus (EWCM) and ovulation strips, can also tell a couple when the sperm should be trying to meet the sperm.  Whether this is through intercourse or through the insertion of donated semen, the timing is important.  BBT charts can only tell you you have ovulated after the fact (more on this below), but after a few months of tracking you can come to see when your fertile window falls. I personally do not think this is the best way to time sperm meets egg, as the EWCM is much more important for timing – the fertile mucus both keeps the sperm safe and helps it to get where it’s going at the right time.  (Read more about this here.). 

Finally, one more use of a BBT chart is to be able to see changes in hormonal health.  A BBT chart is absolutely unnecessary to know if  hormonal health is improving.  There are always other indicators to track, such as quality of sleep, abundance of EWCM, bowels, urination, and most obviously, menstrual symptoms.  However, it can be fun and satisfying for the patient (and your herbalist and acupuncturist, if you have one) to see the chart become more and more textbook each month.  This is not for everyone.  Some people find it fun, some find it stressful, so once you have confirmed that indeed you do ovulate, do as you please.

Okay, I’m ready to try it, how do I do it?

Go to the pharmacy and get yourself a thermometer with two decimal points.  The tenths of a degree is where you will see the temperature fluctuation.  The moment you wake up, before you speak, get up, go pee, sip water, stick the thermometer in your mouth and let it sit there a few minutes so that it is your temperature. Then push the button, wait for it to beep, read the temperature and record it.  You can record it in an online fertility tracker or on a good old fashioned spreadsheet.  (If you like the paper versions I have one free for download here.)  Typically these spreadsheets and apps also have a line to track cervical mucus (CM), when there was sex or insemination, and other data.  (This is highly personal data…this data will also show pregnancies and miscarriages.  If you prefer not to share this with a third party, use Google to find which apps are available currently that commit to storing your data locally only.)  All of these signs together show a complete picture of your fertile window.

But what am I looking for?

Okay, so you’ve done the work, you have a cool graph, but how do you interpret it?  You want to see a “biphasic” chart, which means a clear delineation from a more or less steady line at a lower temperature from the first day of your period (cycle day one) to midcycle, when you should see a clear and distinct stair step of half a degree.  After the temperature rises, it should stay up until right before you start bleeding.  It is the hormone progesterone that increases your body temperature just after ovulation, and it is the withdrawal of this hormone that causes the uterine lining to shed.  If right before your period your temperature does not drop, but instead goes up and stays up another half a degree, this is called a triphasic chart.  Triphasic charts can often indicate pregnancy!

Let’s take a look at a real live charts pulled from public forums on the internet to see what this can look like and how it might change.  

The first one is example of why it is helpful to temp.  The LH surge is occurring (the red line) but the blue line never goes up and stays up about half a degree.

Here is another chart.  I think this one is great to see because it shows both an anovulatory chart at the beginning, and then ovulation. The ovulation is weak in that there is not a clear stair step change that stays well elevated, but still the chart is biphasic.  Someone with an anovulatory chart will see a line that looks like what this chart looks like up until cycle day 32.  This kind of pattern could go on for weeks, even months.  It is not uncommon with a chart like this to periodically get EWCM.  The body is trying to ovulate but cannot.  A skilled herbalist can determine how to help your body and also give you herbs specifically for when you see the EWCM to help the egg release.  

People with long cycles will typically have a chart like this.  There is no reason to be too concerned about a long cycle if everything else is going well (EWCM at ovulation, easy periods, good poops, energy, mood).  A person with a long cycle can still be ovulating and have a healthy luteal phase temperature-wise.  This chart shows that there is more going on than a long cycle.  The temperatures in the luteal phase go up quickly (steeply), which is very positive.  However, the temperature does not go as high as we would like (ideally the temperature goes up half a degree) and has some trouble staying up.  An acupuncturist and herbalist can help regulate your cycle so that you both have more opportunities a year to try for pregnancy and better chances for success.

Here’s another cycle that could use a boost from Traditional East Asian medicine.  The chart is biphasic, but it kind of swoops down into the proliferative phase, and swoops up into the luteal phase, without a strong and steep rise.  The temperature is still dropping into the proliferative phase after the person is done bleeding.  

With treatment, we often see a chart that looks like this turn into a chart that looks more like this:

This is a textbook chart, clearly biphasic.  The chart is in Celsius, and shows more than half a degree rise.  Assuming there are no issues with the sperm, when charts look like this, people get pregnant!

Patients often ask about random spikes up or down.  If they are one-offs, check to see if they indicate sleep disruption, alcohol use, travel, or illness.  If it is as simple as you got up to pee, mark that and consider it an outlier.  Tracking your temperature can show you how easily a couple of drinks, lack of sleep, or a cold can affect your cycle.

I hope these charts are helpful to you as you deepen your understanding of your own body’s cycles.   Please feel free to share any questions below.