The Basal Body Temperature
The basal body temperature or BBT is an important indicator of the process of ovulation.
I have coalesced in this article the main points I have used in discussing this aspect with women over the years, that will give a basic understanding to every woman about what she needs to know.
What is Basal Body Temperature?
Any benefits measuring and charting the BBT? With regards to the menstrual cycle, the BBT has important practical utility.
- For a woman to become pregnant, she must ovulate. Fertility charting using the BBT charting is an easy way a woman can determine for herself if she is ovulating or not. BBT can thus be used in infertility evaluation.
- Charting the BBT can be used accurately to determine the time of ovulation.
This is of utmost importance to women seeking a pregnancy for fertility awareness. However, you may use ovulation test kits to identify the ovulation day if you do not want to use the BBT chart.
- BBT charting is a simple and reliable way to determine the length of the different phases of the menstrual cycle. This is most important for the determination of the luteal phase. An adequate luteal phase length is necessary to sustain an early pregnancy.
- The basal body temperature can also be used to suspect a pregnancy. Persistent temperature elevation beyond the usual length of the luteal phase should prompt a pregnancy test!
All menstrual cycle changes are caused and preceded by changes in hormones.
Estrogen is the major hormone of the follicular phase while progesterone is responsible for most of the changes of the luteal phase.
These two hormones, in addition to their usual structural effects, also influence the basal body temperature. Generally, the high estrogen levels of the follicular phase cause a slight decrease in body temperature while progesterone in the luteal phase causes a slight elevation.
Normal Basal Body Temperature
The normal BBT for a menstruating female shows a characteristic variation from the follicular to the luteal phase. Normal values are slightly higher during the luteal phase.
Measuring the BBT
Many women are familiar with body temperature measurement especially to document the presence of fever. They are most probably familiar with the ordinary fever thermometer. A woman may need to measure the basal body temperature for any of the reasons listed above.
For higher accuracy and usefulness, the following should be taking into consideration during the measurement procedure:
- The BBT should be measured first thing in the morning, even before brushing the teeth! In fact, while you are still in bed.
- Do all to measure it about the same time each morning.
- Use the same site. The mouth is a good site for this purpose for reasons including accessibility and relative accuracy.
- Do not change the thermometer, except it gets bad or something similar happens. Do all to keep all things about the same for each measurement.
The changes in BBT that have to be detected are not really great and can be easily missed by an ordinary fever thermometer. Special thermometers now called basal thermometers are sold in drugstores, separate from fever thermometers.
Basal thermometers need to have an accuracy of at least 0.1°F (0.05°C) to effectively measure the BBT changes during the cycle. Today, both mercury-in-glass and digital basal thermometers are available. Get the one most convenient for you.
Once measured, the basal body temperature should be charted. That could mean the thermometer, a pencil or pen and a chart should be by the bedside. No matter how you decide to do it, remember to write is down as soon as you read the temperature.
A ovulation chart is simply a paper that you record the temperature readings. It could simply be for BBT only for woman monitoring only this sign or be associated with other signs like cervical mucus. You can download our free ovulation chart for personal use. Always remember that you are different and so what worked for a specific individual may not be exactly the same with you.
Interpreting BBT Chart
After having the figures before you, what next? What does that graph mean?
Interpreting the BBT chart is usually not difficult. Remember that all is centered on the process of ovulation.
- The most important recommendation for every woman charting the BBT is that she learns to identity a pattern of her BBT variation predicting ovulation that is specific for her. She might need a minimum of about 3 to 6 months to be certain of this pattern.
- The BBT shows a sustained rise only after about 2 to 3 days after ovulation. So the rise in BBT only tells you ovulation has passed. It is not predictive but retrospective within each cycle. However, learning the pattern over months may enable a woman to predict ovulation even before it occurs.
- For woman having fertility problems, noting the sustained rise in the basal body temperature during the luteal phase is an indication that she is ovulating.
A few cautions about BBT charting
- Remember that abnormally high temperatures above normal may indicate an infection.
- Inconsistency in time of measurement or rest may produce inaccurate results.
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