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Fluctuating temperatures


Why are my basal body temperatures fluctuating so much?

Erratic Temperatures

Interpreting the variations of your basal body temperature can be a challenging task, especially when no clear pattern is visible.

Large fluctuations in your BBT can easily mask your fertility pattern and are usually due to a few factors. Let's review the most common issues:

Inconsistent Timing

If you do not take your BBT within about 20 minutes day to day you may observe variations in your BBT reading that are due solely to your body’s metabolism. We recommend to simply use an alarm clock to time your temperature observations.

Incorrect temperature taking method

We recommend to take your temperature orally by placing the tip of the thermometer under your tongue and towards the back of your mouth. Other methods of taking your temperature for fever temperatures such as using armpit, ear or skin thermometers are not recommended. It may cause large variations in your BBT, rendering any interpretation inaccurate.

Some women find that taking their BBT vaginally may lead to smoother readings. This is also an option in Fertility Friend.

Sleep Patterns Issues

The recommended guidelines for taking your BBT is to take it right when you wake up and after a solid block of sleep whenever possible.

External Factors

Illnesses, medications and other environmental factors may influence your temperature pattern. We recommend to record anything unusual on your chart. You can use a note or make a custom data entry if it occurs frequently. You will then be able to identify these disturbances and see if they interfered with your interpretations.

Thermometer issues

We recommend to use a digital basal body temperature thermometer. If your pattern is very clear, an accurate digital fever thermometer may be adequate. If you are using a wearable device to measure your BBT, make sure that it actually measures BBT and not just something resembling a temperature.

Hormonal Factors

Temperatures can also fluctuate a great deal when you are not ovulating, or when you have cycles with delayed ovulation. In this case the pattern is actually a clue as to what is going on.

If you are taking your temperatures accurately and are still having large temperature fluctuations with no clear ovulation pattern over a few cycles, this should be mentioned to your health care provider. This is especially important if it is taking longer than expected to conceive.

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