This article is the first in a short series of articles about basal body temperature (BBT) monitoring for fertility, and how it can be useful for highlighting imbalances in the body from the point of view of Chinese Medicine.

We recommend BBT monitoring for all our female fertility patients. The reason is simple - it gives a unique window into the body's monthly rhythms that can augment the usual health information obtained during ongoing treatments. Some patients find it a little hard to get used to having to take their temperature first thing in the morning, every morning, but most find that once it has become a part of their daily rhythm it is no more trouble to do than brushing their teeth or making breakfast.

The basal body temperature (BBT) records the body temperature on waking, at a time when the body is in a well rested state. Once the body is out of bed and active, the body temperature rises from this baseline level so to get an accurate reading of the BBT it is important that the temperature is measured as the first thing after waking. Ideally it needs to be taken at the same time every morning because the basal temperature can rise by roughly 0.1 degree for every delayed hour rising. However, given this knowledge it is possible to correct the recorded temperature if the waking time does vary, and could also increase in the case of medical conditions, so is important to learn of doctors who accept new patients and can treat these medical conditions at home.

Chinese Medicine aims to determine the state of health of the internal body based on careful observation of external body signs and symptoms. For example, observations of the colour of the complexion, the colour and shape of the tongue, the nature of the menstrual blood or the speed and strength of the pulses at the wrist, can be combined into an overall diagnosis of internal imbalances that could be contributing to the infertility. The BBT is a more modern yet very instructive sign, as it is intimately related to the menstrual cycle itself. In particular, the change in hormones that occurs as a result of ovulation (i.e. an increase in progesterone) causes a shift in the average basal body temperature. This shift can be seen in a typical chart shown in figure 1 below, where the BBTs average around 36.1 for the first 15 days but then jump up to average around 36.6 degrees after ovulation for the whole second half of the cycle.

BBT graph1-1

If pregnancy occurs the BBT will stay high, but if there is no pregnancy the temperature will drop again to the lower level once the period arrives. It is important to note that the temperature rise occurs after ovulation has occurred so on its own the BBT will only show the end of the fertile part of the month, not the best time to have intercourse.

The egg itself is only fertilizable for about 6-12 hours once it has been released. In contrast, sperm can survive up to 5 days once inside the female reproductive system, so ideally there should be plenty of healthy sperm in the fallopian tubes ready to fertilise the egg very soon after it is released. The most fertile time is therefore some time before ovulation has occurred.

If the cycle is regular, knowing when the temperature rise will happen allows a woman to predict approximately when her fertile time is (a few days before the rise). To determine the most fertile time of the month, the BBT should be combined with careful observation of the cervical mucus and/or information on the LH surge as determined by ovulation predictor kits.

In the next article in this series, we will look at the different types of BBT chart patterns and what they say about different imbalances inside the body from the point of view of Chinese Medicine.

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