The basal body temperature is your body temperature at rest, usually taken as soon as you wake up in the morning. Women trying to get pregnant often take their basal body temperature, or BBT, every morning to watch for the drop in temperature that occurs just before ovulation. After ovulation, the BBT rises and remains high until it either drops at the time of the next menstrual period or remains elevated, indicating pregnancy. Reading a basal body thermometer and recording accurate results is essential to ensure accuracy. While digital thermometers are easy to read, glass thermometers, with or without mercury, require more practice.
Before Using
Step 1
Purchase a specialized BBT. Glass basal body thermometers record a narrower range of temperatures, usually 96 to 100 F, so that the thermometer can be marked in lines indicating 1/10 of a degree rather than the 2/10 standard on most glass thermometers. Buy a mercury-free glass thermometer, because mercury can cause health issues if the thermometer breaks. You may have more luck finding a mercury-free glass BBT online rather than searching the pharmacy for one.
Step 2
Remove your BBT from the packaging and get familiar with it. Many people today have never seen, much less used, a glass thermometer. Glass thermometers can be difficult to read unless you hold them at the right angle, so that the silver line is visible. Holding the BBT in front of you with the numbers facing you, move the thermometer slightly until you see the silver line clearly.
Step 3
Familiarize yourself with the numbers. The degree--96 F, 97 F, and so on--is printed on the thermometer. In between the whole numbers are nine shorter lines, each representing 1/10 of a degree. Read the temperature where the silver where the silver line stops. So if the silver line goes past 97 F and stops at the third line, your temperature is 97.3 F.
Obtaining Reading
Step 1
Place the BBT in your mouth, under your tongue, as soon as you wake up and before any physical activity. Alternatively, you can take your temperature rectally or under the armpit, or axillary, but axillary readings may not be as accurate and take longer. Taking a rectal temperature may not be comfortable and may also require that you get out of bed, which can raise your temperature. Any movement at all can raise your temperature, so make taking your temperature the first thing you do.
Step 2
Keep the thermometer under your tongue for five minutes. Glass thermometers don't beep, so you need to leave it in place long enough to obtain an accurate reading. Don't get out of bed or do anything while you're waiting.
Step 3
Remove the BBT from your mouth, turn it so you can see the silver line and determine where the line stops. Record your temperature on your BBT chart and wash your thermometer so it's reading for the next reading. Shake it down so it's ready to use in the morning without any physical effort on your part.
Step 4
Put the BBT away. Keep it in the plastic container it came in so it doesn't break if it falls on the floor. Store it next to your bed so you don't have to search for it the next morning.
Tips and Warnings
- Practice taking your temperature a few times before the morning you record your temperature, to get familiar with the process. If you use a digital thermometer, keep extra batteries nearby, in case they die mid-reading. Take your temperature at the same time each day, if at all possible.
- If you're using an old mercury thermometer, don't touch the mercury with your fingers if the thermometer breaks. Always use the same thermometer for daily readings.
Things You'll Need
- Basal body thermometer
