There are two types of thermometer in common use:-

  • Glass / mercury fertility thermometer
  • Digital thermometer

Fertility Thermometer

This mercury and glass thermometer is like a clinical thermometer, but it covers only the range from 35-39 deg. C.

This makes it easier to detect the minimal changes which occur.

Because of its fragility, special care has to be taken in using the fertility thermometer.

A woman should have two fertility thermometers available in case of breakage.

(The use of a new thermometer should be recorded on the chart).

  • It must never be put in hot water
  • It should not be used if a woman suspects she has a fever
  • It should be kept away from children
  • Care must be taken when shaking it down after use.
    The mercury should be shaken down below 35 deg. C the night before.

The time taken to record the temperature :-
  • Oral temperatures - 5 minutes
  • Internal temperatures (vaginal or rectal) - 3 minutes

Fertility thermometers are not allowed on aircraft,
because they contain mercury.

Digital Thermometer

Battery-operated digital thermometers are now chosen by many women because although they are more expensive, they are safer, being virtually unbreakable and there is no restriction on air travel.

They are easy to read and the recording time is reduced.

Digital thermometers give an audible bleep when the temperature has stabilised (after about 1 minute). This useful feature avoids the need for clock watching.

Many digital thermometers also have a ‘last memory recall’ feature. This is particularly useful as it avoids the necessity for recording the reading immediately if this is inconvenient.

It is important to follow the manufacturers instructions and replace the battery as indicated.

Return to 'Temperature - a Fertility Indicator'

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