What is Basal Body Temperature?
Basal Body Temperature (BBT) is the temperature of the body on waking – when the body is rested, and metabolism and temperature are at a baseline. The BBT has been used in the past to identify the times when a woman is ovulating in order to either encourage or avoid conception. This is possible because there is a (relatively) reliable variation in the body temperature through the menstrual cycle due to hormonal changes. However, not all women follow the typical pattern, and the method is not sufficiently reliable to use as a form of contraception.
An example BBT chart is shown below:
There are two main phases during the menstrual cycle – the follicular phase (pre-ovulation) and the luteal phase (post-ovulation). The temperature is normally lower during the follicular phase, raising rapidly soon after ovulation. The temperature then remains at a higher level during the luteal phase, reducing again around the time of menstruation. It is therefore possible to estimate the time of ovulation to be around day 14 on the chart above.
In Chinese medicine, the BBT chart can be used for more than estimating the time of ovulation. The average temperature during each phase, the rate and extent of the rise and fall in temperature, and the general shape of the chart all give information on the prevailing energetic patterns. This means the BBT chart can be useful in clarifying the diagnosis in cases where there is any kind of abnormality in the menstrual cycle (short, long or irregular cycles, painful or no menstruation) or if there are early menopausal symptoms.
There are other signs and symptoms that can be charted alongside the basal body temperature. These include menstrual flow and spotting, quality of cervical mucus, severity of any abdominal pain, breast soreness or swelling and any other symptoms that may be relevant, such as emotional changes. Each of these signs and symptoms provide further valuable information to clarify the diagnosis.
How to chart your BBT
Basal body temperature must be measured first thing in the morning, after at least three hours of uninterrupted sleep, and before you get out of bed or do anything else. Take your temperature and plot it on the chart first thing in the morning – it helps to keep both the thermometer and chart next to your bed. At the end of the day, make a note of the other signs and symptoms you’ve experienced. It’s especially important to note if you are ill or drink alcohol (which will raise the temperature) or taking painkillers (which may reduce the temperature). If you sleep later than usual, your temperature may have risen, so this is worth noting on the chart as well.
You will need to use a basal thermometer as normal thermometers are not accurate enough to measure the small temperature changes. You can buy basal thermometers from pharmacies or search online. They should only cost a few pounds.
BabyCentre (www.babycentre.co.uk) has lots of articles on fertility, pregnancy and early childhood, including:
Lyttleton, J. (2004) Treatment of Infertility with Chinese Medicine.