What is the basal body temperature?
The basal body temperature is the lowest normal temperature (i.e. without any illnesses or abnormal environmental conditions).
Why record the basal temperature?
The two most common reasons to record your basal temperature is to provide information about thyroid function (people with under-active thyroid may be ‘colder’ than typical) and to monitor a woman’s reproductive cycle and help with preventing or achieving pregnancy.
Charting in reproduction
Women have two cycles that occur simultaneously: a menstrual cycle (following what is happening to the lining of the uterus, the endometrium) and an ovulatory cycle (following what happens with the ovaries and what hormones are produced). During the ovulation cycle, women usually have a biphasic temperature pattern (that is, there are two phases). The first phase is the follicular phase and lasts from commencement of menstruation to ovulation. The second phase is the luteal phase and this lasts from ovulation to menstruation. After ovulation, the ovary produces higher levels of progesterone and this increases the temperature during the luteal phase. The increase in temperature is only small, around 0.2 degrees Celsius, but this increase is useful to determine that you are ovulating normally. Note; it is possible to still have a period even when you have not ovulated, or if you have not ovulated normally.
How to take you Basal Body Temperature
Because the change in temperature is so small, it’s important to take your temperature at the same time every morning, before you get up or move.
- Be prepared – keep your thermometer by your bed, where you can pick it up without getting out of bed or even sitting up. Getting out of bed or even sitting up can throw off your temperature and skew the results. If you use a mercury thermometer, be sure to shake it down before you go to bed at night.
- You should try to take your temperature at the same time every morning, with no more than a 30 minute difference from morning to morning.
- When you wake up, reach for your thermometer and take your temperature. Do not sit up or get out of bed, even to go to the bathroom.
- You can take your temperature orally or vaginally. It doesn’t matter which way you choose, as long as choose one and stick with it. If you tend to sleep with your mouth open, taking your temperature vaginally may be better.
- Follow the directions for your thermometer to get the best reading. If you’re using a mercury thermometer, make sure you leave it in place long enough to get an accurate reading -that may take up to eight minutes.
- After you take your temperature, write it down.
In the chart above, you can see that even though there is variation between the days, the first half of the month the temperature was lower than the second half of the month, and this person would have ovulated on Day 14 of her cycle.
Tips
- If you need to wake up extra early, or later than usual, take your temperature as you always do and mark the difference in time on your chart.
- You should use the same thermometer throughout the cycle. If you buy a new one, start using it on day one of the next cycle.
- You need to have slept at least four straight hours for your temperature to be accurate. If you get up often at night to go to the bathroom, or have trouble sleeping, this can affect your results. You should take your temperature anyway, and note on your chart that your sleep was interrupted.
- While basal body temperature charting can pinpoint when ovulation occurred, it isn’t a good way to predict ovulation. For additional information, especially in predicting ovulation, it is useful to include other observations, such as cervical mucus texture and volume.
Conditions affecting your temperature
There are a number of things that can ‘throw off’ your charting, the most common being: illness, stress and poor sleep. Even a simple cold can alter our temperature, making it difficult to accurately chart your basal temperature. If you breathe through your mouth when sleeping this can also alter your oral temperature. If your sleep in or get up early also can change your reading. If any of these things occur, simply make a note of them on your chart so that you can take them into consideration when interpreting your chart. If the problem is chronic, such as blocked sinuses or stress-related insomnia, now is the time to address those things.
Image references
Chart: www.baby4you.co.nz
