What is it? "Basal" means "of or forming the base". "Basal metabolic rate" is "the rate at which heat is given off by an organism at complete rest". And "metabolism" is "the chemical changes in living cells by which energy is provided for vital processes and activities and new material is assimilated [broken down and gotten into the system]". So, "basal body temperature" ("bbt") is the temperature of the body when it's at complete rest. In other words, it is the actual temperature of the body without any other modifying factors which could raise or lower the temperature, such as moving around, eating and drinking, being in a hot car, and so on.
What can you do about it? In order to get a good basal body temperature reading, one should take one's temperature directly upon awakening in the morning, hopefully after having had at least three consecutive hours of sleep. Take your temp before getting up to go to the bathroom, before drinking or eating anything – in short, take your temp before you do anything. Try to always take your temp at approximately the same time each morning, since what is important here is not so much what the actual temperature is, but whether it's gone up or down from the previous day, and by how much.
It's easiest to use a digital thermometer, since it's faster. If you do decide to use a non-digital thermometer, make sure you shake it down the evening before. It is preferred to use a thermometer (either digital or otherwise) specified as a BBT thermometer, because they tend to be more accurate. If one is just taking one's temp to see whether one has a fever, it doesn't really matter if the thermometer is off a little bit or not (for example, you know you have a fever if it's 100-something, and who cares if it's 100.1 or 100.3?). However, for the purposes of BBT charting, one is very interested in the range of the temperatures – did it go up or down when compared to yesterday's temp, and by how much? – so accuracy is desired. The thermometer does not need to go to two decimal points (i.e., 98.00); one decimal point (i.e., 98.0) is sufficient.
There are several brands of BBT thermometers. My favorite is the Omron brand: other brands beep constantly and loudly until they are finished, but the Omron digital BBT thermometer only beeps when it's done, and it's much quieter – so you don't end up waking up the rest of the house!
Charting your temps. You can either manually chart your temps on some graph paper (homemade or purchased), or you can use one of several online charting services (some of which are free).
What does it mean? Before a woman ovulates, the basal body temperatures range from around 97.0 to 97.5 degrees Fahrenheit (36.1 to 36.3 Celcius). This is due to the presence of estrogen, which keeps temps down. Once ovulation has occurred, the temps go up to a new, higher level, usually ranging from around 97.6 to 98.9 F (36.4 to 36.6 C). The rise in temps to this new, higher range after ovulation occurs due to the presence of progesterone, which is being created by the corpus luteum on the ovary. Temps will stay in that range until the next menstrual period. The temps often drop just before menstruation, thus acting as a "red flag" (sorry for the pun) that one's period is on the way. However, this is not always the case, and the temps often do not drop until a few days into menstruation.
Why should you temp? Temping is only useful to help determine that ovulation is occurring, at what point in one's cycle ovulation is occuring, and whether one's luteal phase is sufficient in length. It does not tell one that ovulation is going to occur, although some women experience a substantial temp dip on the actual day of ovulation, which is due to a surge of estrogen which often (but apparently not always) occurs just prior to ovulation. But this is not a sure thing, and one really just cannot forecast ovulation by one's temps.
The day after ovulation, the temp generally jumps up by at least 0.2 degrees F (0.11 degrees C), and then continues to rise somewhat. It will become apparent after a few days that it is in a new, higher range. The temps themselves will continue to rise and dip day by day, but will remain in the higher range. Some women experience a slow rise over a period of days rather than an immediate rise, which makes it more difficult to ascertain ovulation. However, even with the slow rise, a pattern of temps in a higher range will become evident after several days and one can generally pinpoint the day of ovulation with some degree of accuracy. It is helpful to also take note of other fertility signs, such as cervical mucus and cervical position (discussed elsewhere in this section).
During pregnancy, temps tend to remain elevated.
Once one has a feel for one's cycle through several months of temping, it is not necessary to continue doing so. In fact, many find it to be a very stressful experience, in that every morning they are worried about what one's temp will be – did it go up? did it go down? – and this is especially bad during the 2WW (two-week wait – the waiting period between ovulation and the next menstrual period, or hopefully the discovery of pregnancy).
