Your mercury thermometer should be reset by shaking it down the night before the first morning test, as well as after you have recorded each morning’s result. This ensures the thermometer is ready to use well before the next testing. It can take quite a bit of shaking to get the mercury column to go down to below the 35 degrees Celsius (95.0 degrees Fahrenheit) figure on this type of thermometer. You must take your temperature immediately after awakening as any physical activity will increase your temperature, thus preventing you getting the required basal reading.
As soon as you wake up, take your temperature, under the arm in the armpit, (not under the tongue) for a full 10 minutes. It is vital to place the mercury thermometer underarm and not under the tongue. Do not move or get out of bed before taking your temperature. Any such activity will raise your basal body temperature and make the test less reliable.
It’s important to accurately record the readings, as well as try to have those readings taken at about the same time each morning.
For premenopausal women, it is important to only measure the temperature on the 2nd, 3rd and 4th morning of their menstrual bleeding.
For men and post menopausal women, the temperature can be taken on any 14 – or more consecutive mornings.
Once you have recorded the 14 readings, work out the average temperature.
Understanding your basal body temperature results
A healthy human’s normal body temperature is considered to be 37 degrees Celsius (98.6 Fahrenheit). If your average basal body temperature (BBT) reading is below 36.5 degrees Celsius (97.7 degrees Fahrenheit), then this is an indication, that you have a low thyroid condition. In such cases, a TSH reading (a thyroid test done on a blood sample) is also more likely to come back as over 2.5mU/L.
Celsius and Fahrenheit Conversions
(°C x 9/5) + 32 = °F (°F – 32) x 5/9 = °C
Converting 36.5 degrees Celsius to Fahrenheit: 36.5 x 9 = 328.5
328 divided by 5 = 65.7
65.7 + 32 = 97.7