Your body's temperature is a very sensitive mechanism. As the hormones in your cycle change your body's temperature changes in relation to these hormones. To gauge these changes you must look at the basal body temperature (BBT).

Your basal body temperature gives you a very simple way to chart your fertility. By measuring minute changes in the temperature, you can more accurately predict when you will ovulate in any given cycle. By charting several cycles you can get a feel for this prediction even more accurately.

Looking at your basal body temperatures, you can see temperature shifts and identify potential problems with your cycle as well. They can reveal a short luteal phase. They can even potentially predict a pregnancy. Basal body temperatures are a source of a whole host of information.

Equipment

To begin taking your temperature you must first get a basal body thermometer. The difference between this thermometer and a fever thermometer is that the basal body temperature thermometer registers your temperature in .1 degree increments. A fever thermometer usually uses .2 degree increments. Since you want to measure minute changes in your temperature, it's best to use the most accurate thermometer possible.

You can use a glass thermometer or a digital thermometer. The benefits of using the digital thermometer over the old-fashioned glass thermometer are that the digital ones usually register your temperature faster.

Methods

To begin taking your temperature you need to decide how you are going to take it and do it the same way every morning. You must wait until the start of a new cycle before making any changes in your procedure, because body temperatures vary slightly from place to place.

You have three choices for how to take your temperature: orally, vaginally, or rectally. It is important to measure your temperature at the same depth or location each time. For example, if you always put the thermometer under the left side of your tongue, continue measuring that same side throughout that entire cycle.

It is imperative to take your temperature first thing in the morning. Do not go to the bathroom first. You should not even speak. Every movement you make increases your basal body temperature. Minimize your movements. This increases your ability to get an accurate reading. And while you can't always get a great night's sleep every time, remember the golden rule: You must have slept for at least 3 hours before taking your temperature. Five hours of uninterrupted sleep is best.

You should attempt to take your temperature at the same time every day — this includes the weekends. This may mean setting your alarm on weekends. The accuracy is worth the effort. Your temperature is most accurate if you take it within a half an hour before or after your designated time. So, for example, if the time you have chosen to take your temperature is 7:00 A.M., you should try to take your temperature each day between 6:30 A.M. and 7:30 A.M.