Basal body temperature (BBT) charting is one of the three major ways that you can monitor your cycle on a daily basis, along with cervical mucous and LH strips. Cycle monitoring assists with predicting the correct timing of intercourse to maximize your changes of conception.
You will need to purchase a BBT thermometer, which is usually available at your local pharmacy. The package should say “basal” or “fertility” on it, and it should be an digital oral thermometer that ideally reads to two decimal places (ie. 36.45°C). I like to use Fahrenheit instead of Celsius because it offers more specific temperature readings. Keep your thermometer somewhere within easy reach of where you sleep.
To chart your temperature, I recommend that you use an App on your phone or online. There are many free Apps available that help to organize and track your cycle monitoring. If you feel more comfortable using pen and paper, create a graph outline similar to the example below (Figure 1). Day 1 corresponds to the first day of your last menstrual period.
Figure 1: Sample BBT chart
How to measure BBT
Your BBT must be measured immediately upon waking. Moving around will raise your body’s temperature and affect the accuracy of your reading. Instead, keep the thermometer in an accessible place so that you can reach over and take your temperature immediately upon waking.
Measure your temperature by placing the BBT thermometer under your tongue and closing your mouth. Wait until the thermometer beeps to indicate it has finished before removing it from your mouth to check the reading. Immediately record the result on your fertility chart.
In order to ensure accuracy of BBT readings, the following must be taken into consideration:
1. Your BBT should be taken at the same time each day
2. You must have slept for a minimum of three hours
- Keep notes of the time you take your BBT every day, and under what circumstances (ie. toddler woke you up one hour early)
3. Take your BBT immediately on waking, before getting up and moving around.
- Do not eat, drink, or smoke before taking your BBT
4. Use the same thermometer each day
5. If your BBT is inconsistent or does not show a clear pattern, talk to your Naturopathic Doctor about taking BBT vaginally, and consider lab testing to better understand your hormonal patterns.
6. Many other things can influence your BBT. Note them in your chart:
- Fever, cold, sore throat, illness
- Alcohol intake
- Smoking cigarettes
- Medications (over the counter or prescription)
- Recreational drug use
- Emotional or physical stress, excitement, depression
- Sleep disturbances (poor sleep, upsetting dreams, insomnia, restless leg)
- Heating pads/electric blankets – avoid, but if necessary keep at the same heat setting, use nightly, and record it in your notes.
- Jet lag, travel, change of room temperature or climate
How does BBT work?
Your BBT should be slightly lower in the first half of the cycle, from day 1 until ovulation, and will rise after ovulation due to increased levels of progesterone in the body. Progesterone is produced by the corpus luteum, which is the egg that has been released during ovulation.
At ovulation we look for an increase of about 0.4°F or 0.2°C, but your body’s temperature increase might be as subtle as 0.2°F or 0.1°C. Typically, we know that ovulation has occurred when the temperature rise is sustained for at least three days. After ovulation, temperature should remain elevated for 10-16 days, and drop significantly before the start of your period. This is because the corpus luteum regresses and stops producing progesterone if it is not fertilized, and this indicates to the body that the uterine lining should be shed. If you are pregnant, progesterone continues to be produced and the temperature remains elevated.
The key is that ovulation occurs the day before temperature rises. You are most fertile in the three days leading up to, and the day of ovulation. BBT is most helpful when used consistently for a period of at least 3 months so that you can recognize your pre-ovulatory temperature patterns, and thereby predict when ovulation is likely to occur.
Other benefits of BBT monitoring
BBT can be helpful for monitoring your cycle in a detailed way. It is helpful for determining if you ovulated at all, as some cycles are anovultory, meaning no follicle was released. BBT can also assist with determining if you have high enough levels of progesterone during the second phase of your cycle (the luteal phase) to sustain a pregnancy. This can also be determined with lab testing, but BBT is helpful for monitoring your progesterone on a daily basis over the long term.
Your Naturopathic Doctor uses your BBT as part of the whole picture of your fertility monitoring. It can help determine which course of treatment might be most effective for you to give you the best chances for conception.
By: Dr. Hilary Booth, ND
Dr. Hilary Booth, ND is a licensed and registered Naturopathic Doctor with a specialty in women’s health, fertility, and pregnancy care. She uses leading-edge evidence-based treatments to provide personalized, compassionate care for her patients. You can reach Dr. Booth at www.drshawnadarou.com.
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