Charting Your Basal Body Temperature
How to Use Your BBT to Understand Your Cycle and Get Pregnant
What Is Your Basal Body Temperature?
Your basal body temperature is the measure of your metabolic activity when you're completely at rest. By measuring your temperature every morning you’re able to see how various hormones are interacting and affecting your period and fertility.
This is a useful tool for confirming ovulation, recognizing diagnostic patterns, early detection of pregnancy, and observation of treatment progress over time.
When To Take Your Temperature
In order to get an accurate measure of your base metabolism it’s important to take your temperature before doing anything else. Talking, drinking water, or moving about too much will cause a change in your temperature that can be confused with ovulation.
Keep your thermometer within arms reach of your bed and plan to take your temperature at the same time everyday. Your temperature will naturally start to rise as the morning goes on and taking it at the same time everyday ensures that the patterns we’re seeing are an accurate representation of changes in your base metabolism.
Temperatures taken with less than four hours of consecutive sleep may not give an accurate representation of your basal body temperature. If your sleep was disrupted, take your temperature and make a note of the poor sleep.
It’s important to take your temperature as soon as you wake up each morning.
Ideally, at the same time everyday for best accuracy.
What Does Your Basal Body Temperature Tell You?
Before Ovulation: The Follicular Phase
The first half of your cycle is called the follicular phase. At this time of your cycle, an ovarian follicle begins to grow and mature in preparation for ovulation. Good follicular development is important because after ovulation the follicle becomes a temporary gland called the corpus luteum. This gland produces the progesterone needed to sustain early pregnancy and alleviate many common symptoms of PMS.
During the follicular phase your average basal body temperature should remain consistently lower - somewhere in the 97.2-97.4F range. Temperatures higher or lower than this range or that fluctuate up and down indicate various hormone imbalances.
Monitoring Your Cervical Fluid
Around the middle of your cycle, you should begin to notice the appearance of and increase in clear, slippery, stretchy cervical fluid. As your estrogen levels rise and ovulation approaches, the cervical fluid that normally helps to keep your cervix closed and secure against foreign bodies, begins to thin.
This thinning fluid plays an important role in conception by protecting sperm from the natural acidity of the vagina, forming channels that allow sperm to efficiently enter the cervix, uterus, and Fallopian tubes to meet your egg, and nourishing the sperm for up to five days as they complete their journey.
If you don’t notice a significant amount of this fluid as you approach ovulation it may be an indication that your estrogen levels are out of balance.
The appearance of this clear, slippery, stretchy cervical fluid is the best indicator for the timing of sex. After ovulation, your egg is only viable for about 24 hours. And because it’s impossible to accurately predict when ovulation will occur, observing physical signs that it’s approaching or passed and having the sperm “pre-loaded,” so to speak, increases your chances of sperm and egg coming together at the appropriate time.
Ovulation and Post-Ovulation: The Luteal Phase
As your follicle and egg reach maturity your estrogen levels are at their peak. This can cause a slight dip in your basal body temperature right before ovulation.
After your mature egg is released from your follicle and ovulation has occurred, the follicle becomes a temporary gland. This gland is called the corpus luteum and produces the progesterone needed to thicken your uterine lining in preparation for conception and implantation.
Progesterone is also calming to the nervous system and improves mood and memory. It helps to moderate the effects of high estrogen and reduce the tendency towards estrogen dominance. It plays a role in healthy bone maintenance, promotes healthy skin, hair, and nails, and supports proper thyroid function. So even if you aren’t trying to become pregnant, regular, healthy ovulation is good for you!
At this time you should see your basal body temperature rise by about one degree due to the increased progesterone. Your temperature should remain stable and ideally above 98.2 degrees until your period arrives. If your period is late and the temperature remains high, this can be your first indicator that you’re pregnant.
Temperatures that are low, unstable, or that drop before the end of your cycle all indicate problems with progesterone production.
Regular ovulation is important whether you’re trying to get pregnant or not.
Healthy ovulation is the main source of progesterone which plays a role in mood, bone strength, thyroid function and health skin!
The Big Picture: BBT Charting is a Tool, not a Verdict
Basal body temperature charting is a useful tool for observing the overall patterns of your menstrual cycle. Don’t get hung up on the individual day’s temperatures, it’s the general patterns over time that are most meaningful. And know, that whatever is showing up in your chart is merely a snapshot of this particular cycle. With acupuncture, herbs, and lifestyle changes, your BBT chart and your hormone balance will shift over time.
There are several things that can cause your temperature to fluctuate that aren’t hormone related:
Mouth breathing caused by blocked sinuses or snoring causes lower temperatures
Alcohol consumption can raise temperatures
Traveling to different time zones can cause inaccurate temperatures until your circadian rhythm adjusts
Fevers will increase your temps and fever-reducing medications, such as acetaminophen and ibuprofen will lower your temps
Long-term use of anti-inflammatory medications or sleeping aids will cause unstable temperatures
Technical difficulties can occur with thermometers - In digital thermometers, batteries eventually run out and temperatures will look lower than normal as the battery life nears its end
A poor night’s sleep and taking your temperature at inconsistent times will cause fluctuations in temperature readings
If any of these things occur, take your temperature anyway, chart it, and make a note.
If you miss a day, make a note and pick back up the following day.
What Kind of Thermometer Should You Use for BBT Charting?
To get the most accurate readings you want to use a thermometer that’s intended for measuring BBT. These thermometers are calibrated to be accurate at normal body temperatures as opposed to the higher temperatures of a fever.
Oral thermometers are most commonly used for taking your BBT, although you could also take your temperature vaginally. Just use the same method for an entire cycle. Some thermometers will save your last recorded temperature so you don't have to chart it immediately. Some will send the data to your phone via bluetooth and chart it in an app. This article links to many of them. Best Fertility Apps of 2020.
You can purchase a thermometer at any drugstore in the family planning aisle, on Amazon, or wherever home health care products are sold. It doesn’t have to be anything fancy, whatever works for you and your budget.
How Long Will You need to chart your BBT?
Consider the first 1 to 3 cycles of BBT charting as practice. You’ll need to figure out the timing of taking your temperature and get into the habit of doing so every morning. There’s a learning curve, so give yourself a lot of grace as you learn this new skill.
How long you chart your BBT depends on what your goals are.
If you’re trying to become pregnant, you’ll want to chart at least until you have a positive pregnancy test.
If you’re charting your BBT to avoid pregnancy, you’ll want to continue charting for as long as you’re trying to avoid pregnancy.
When using BBT charting as a diagnostic tool in the treatment of hormone imbalances and menstrual disorders, you’ll want to chart until your condition is resolved.