April 21, 2015
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Charting your BBT

What is BBT?

Basal body temperature (BBT) is the temperature (to the tenth degree) of your body at rest. Because your body temperature spikes atleast .4 degrees Fahrenheit after ovulation and remains higher after ovulation than it was before until you begin menstrating, you should be able to determine the exact day within your menstrual cycle that you ovulate by charting your BBTs. It may be necessary for you to chart your BBTs for up to three months to be sure outside factors (alcohol, drugs, illness) don't affect your results.

Because your BBT does not spike until AFTER ovulation, it is not likely that you will be able to use your pre-ovulation temperatures to become pregnant, but it will help you determine the length of your luteal phase, which will allow you to adjust your fertility calendar settings if necessary.

Sample BBT Chart

Sample BBT Chart

The image above is a sample BBT Chart for a woman with a 28 day cycle. You can see by looking at the chart that the BBTs of day 8 through day 13 are 97.2, 97.3, 97.8 (which we assume is inaccurate), 97.4, 97.2, 97.3, 97.0 then her temperature jumps to 97.7 and remains high each day until she began menstruating again on day 29. Because of this rise in temperature, we know that ovulation most likely occurred on the day before the rise (day 14). Keeping in mind that the 97.8 on day 10 was inaccurate, a line can be drawn between the highest follicular phase BBT (97.6 on day 1) and the lowest luteal phase BBT (97.7 on day 15), at 97.6. This line (called a coverline) divides the menstrual cycle into two: the follicular phase (shown as day 1-14) and the luteal phase (shown as day 15-28).

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