A sustained rise in the basal body or waking temperature will confirm ovulation. Following ovulation, the hormone progesterone raises the waking temperature by around 0.2 deg.C and maintains it at the higher level until the next period. The rise or shift in temperature helps to identify the start of the post-ovulatory infertile phase.

Temperature readings have no value in predicting ovulation.


RECORDING AND CHARTING THE BASAL BODY TEMPERATURE (BBT)
1.
The temperature should be taken immediately on waking before getting out of bed, drinking tea or any other activity, and at about the same time each morning.

If the recording time varies by more than 1 hour, this must be noted.

2. The temperature may be taken by the mouth, vaginal or rectal routes.
  • Mouth or oral route. The silvery end of the thermometer is placed under the tongue, with the lips closed for the appropriate time.

  • Vaginal route. The thermometer is inserted gently into the vagina.

  • Rectal route. A trace of Vaseline or KY jelly is smeared on the silvery end which is inserted gently into the rectum, while lying on one side with the knees drawn up.

For accuracy, whatever route has been chosen should be followed throughout the cycle.

Oral temperatures usually give satisfactory results if exact instructions are followed, but for some women internal temperatures tend to be more reliable.

3. The chart is marked with the temperature reading by a dot in the centre of the appropriate square. The dots should be joined to form a continuous graph.

If one or more temperature reading are missed do not join non-consecutive dots.

  • Fertility thermometer - If the mercury stops between two marks the lower reading should be recorded.

  • Digital thermometer - Only record the reading to the first decimal place.
5. The thermometer should be cleaned with cotton wool and cold water
6. A new chart is started on the first day of menstruation (fresh red bleeding).

This is Day 1 of the cycle.

If menstruation starts during the day, that morning's temperature should be transferred to a new chart.

7. Anything unusual should be noted on the chart, such as a cold, a late night, drinking alcohol, or any stressful situation.


Return to 'Temperature - a Fertility Indicator'




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