During the luteal phase of the cycle, the corpus luteum produces the hormone progestrone, which elevates the basal body temperature ( BBT) . When the basal body temperature has gone up for several days, one can assume that ovulation has occurred. However, it is important to remember that the BBT chart cannot predict ovulation - it cannot tell you when it is going to occur !
In the past, doctors felt the basal temperature chart was a useful tool. It allowed the patient to determine for herself if she is ovulating as well as the approximate date of ovulation, but only in retrospect. Basal body temperature charts are easy to obtain and the only equipment required is a special BBT thermometer.
General instructions for keeping a basal body temperature chart include the following :
The chart starts on the first day of menstrual flow. Enter the date here.
Each morning immediately after awakening, and before getting out of bed or doing anything else, the thermometer is placed under the tongue for at least two minutes. This must be done every morning, except during the period.
Accurately record the temperature reading on the graph by placing a dot in the proper location. Indicate days of intercourse with a cross.
Note any obvious reason for temperature variation such as colds, or fever on the graph above the reading for that day.
However, the major limitation of the BBT is that it does not tell you in advance when you are going to ovulate - therefore its utility in timing sex during the fertile period is small. Interpreting the BBT chart can be tricky for many patients - rarely do the charts look like those you see in textbooks!
Also, keeping a BBT chart can be very stressful - taking your temperature as the first thing you do when you get up in the morning is not much fun. What is worse is that you start to let the BBT chart dictate your sex life. This is why though the BBT chart used to be a useful method in the past, it's utility is limited today - and newer methods are available which are more accurate are available. We advise our patients never to chart their BBTs - we feel they are just a waste of time.