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How to Fertility Chart
Basal Thermometer and BBT Charting

A basal thermometer is an sensitive thermometer that detects changes in your resting - or basal - temperature. A basal body thermometer is used by women to chart their basal body temperature on a fertility chart and predict ovulation. A digital basal thermometer will typically provide readings to the 100th of a degree and are very accurate.

How Do You BBT Chart?

One of the many changes that take place in a woman's body during her menstrual cycle is an increase in body temperature at the onset of ovulation. During the first the first part of a woman's cycle, the body temperature is lower. With ovulation, the body temperature rises due to an increase in the hormone progesterone and remains higher until the beginning of a woman's next cycle.

Recording each day's body temperature - and charting the pattern of temperature changes - will help pinpoint when when ovulation has occurred and determine future patterns for predicting ovulation. Because BBT charting allows a woman to confirm the onset of ovulation, it is a very useful method in helping facilitate conception - as well as understanding the general patterns and nuances of a woman's menstrual cycle. At ovulation, you will see a temperature shift of at least .4 degrees to a full degree.

This means that your fertility chart should show a low temperature line before ovulation (follicular phase), followed by a temperature spike and higher line after ovulation (luteal phase). A biphasic curve has two phases: It is a curve that rises and stays up after ovulation. The first phase is before ovulation (follicular phase), the second phase is after ovulation (corpus-luteum phase), when temperatures rise because of progesterone. Some women then try to chart a triphasic curve, which has three distinct phases (though the third is not reliable in confirming pregnancy).

- The first phase of lower temperatures before ovulation (follicular phase),
- The second phase of higher temperatures after ovulation (corpus luteum phase). At ovulation the basal body temperature rises and stays up because of the progesterone hormone, which is being produced by the corpus luteum and increases the BBT.
- The third phase, where the BBT curve again rises to a third level (triphasic) of temperatures about a week or so after ovulation.
- The triphasic curve supposedly shows implantation. Many typical pregnancy curves are not triphasic, and many women who have triphasic curves turn out not to be pregnant.

Tips for Using Your Basal Thermometer

Use your basal thermometer first thing in the morning before leaving bed. Do not get up, read, drink water, or do anything. Basal refers to base or resting temperature, so if you would like to accurately bbt chart, stay in bed without movement until you have your result. Try to take your basal temperature the same time everyday, if possible. Ideally, take your basal temperature after at least 5 hours of sleep.

Please remember that BBT charting only tells you when ovulation has already occurred - and is therefore important for predicting general patterns. To predict ovulation ahead of time, you may also consider using a fertility monitor.

Related Articles
Predicting Fertility
Pre-Seed Facts
Pregnancy Info


Predicting Ovulation

• Ovulation Calendar (tool)
• The Anatomy of Ovulation
• FAQ: How can I tell that I'm ovulating?
• Fertility Charting and Methods of Predicting Ovulation
• Charting Ovulation to Pregnancy
• How to Fertility Chart: Basal Thermometer & BBT Charting
• How to use your basal thermometer
• BBT Charting & Timing Intercourse
• Progesterone, Ovulation & BBT Charting
• FAQ: What is "fertile cervical mucus?
• FAQ: How much will my BBT increase?
• FAQ: Can the position & feel of my cervix tell me if I'm ovulating?
• Printable Fertility Chart
• Changes in Fertile Cervical Mucus
• Am I Ovulating?
• FSH and Fertility: How Follicle Stimulating Hormone Can Affect Your Ability to Conceive