Your basal body temperature is your temperature when you’re fully at rest. Your basal body temperature changes approximately .5 to 1.5 degrees during ovulation. You will be the most fertile approximately two days before your body temperature rises.
It is important to use a good basal thermometer to keep track of your basal body temperature. They have digital ones that can keep track of your recording for you (some using a smartphone application), but I suggest just having a small notepad in the bathroom and keep track that way as well, to avoid any errors. Some of these thermometers will keep your recording, but it is usually only until the next time you use it, so make sure you (or ask your partner for help) write it down right away. Also, it is extremely important to check your temperature the very moment you wake up in the morning. It would also be very helpful if you could maintain the same routine every day and check your temperature at the same time every day. If for some reason this pattern gets interrupted, it would be good to make note of that on your chart.
Some even say to take your temperature before even getting out of bed. This may be uncomfortable for some women, so if you have to make it to the bathroom, that’s okay. Just make sure you take it nice and easy to the bathroom and don’t do anything dramatic that would make your body temperature change too much. Also, temperatures can be taken orally or vaginally. But whatever method you choose, make sure to keep it consistent throughout the time you are tracking your temperature. Most women probably prefer to take their temperatures orally, but when temperature patterns are unclear, switching to vaginal for the next cycle sometimes makes the pattern clearer. Also, if you have to use a heated mattress pad or blanket to stay warm (thank you midwest) make sure to keep it on the same temperature or setting while keeping track of your basal body temperature, that way it won’t skew any of the results.
There are certain things that could affect your basal body temperature, including but not limited to: fever, infection, cold, sore throat, alcohol, drugs, smoking, physical stress, excitement, travel, change in climate, etc. Make sure to note any of these things while keeping track of your temperature to ensure proper readings.
Using your basal body temperature can also be used to detect pregnancy. Following ovulation, a rise in basal body temperature that lasts for 18 or more days may be an early indicator of pregnancy.