How is basal temperature measured? Practical guide
7 rules for measuring basal temperature correctly and obtaining useful graphs for recognizing ovulation and fertile days.
The basal temperature method to identify the fertile period requires a lot of precision and constancy. The more accurate and regular the measurement of body temperature is , in fact, the more reliable the method will be.
But how is basal body temperature measured? Can I use a normal thermometer or do I need a specific one? Can the measurement be performed orally or under the arm ?
To answer all these questions, we thought we’d create a small practical guide on how to measure basal temperature correctly.
With these few simple rules , you will be able to compile your graphs and save them in your personal area .
Also, if you wish, I could compare you with other more experienced readers on our forum dedicated to basal body temperature .
1) Use a suitable thermometer
If you’re wondering if basal temperature can be measured with a regular thermometer , the answer is yes , although it would be preferable to buy a digital thermometer to two decimal places .
In fact, to obtain an accurate measurement, it is important that the thermometer is sensitive enough . Nothing therefore prevents the use of a common mercury-free glass thermometer , which has a sensitivity of 1 tenth of a degree.
However, where conventional thermometers will register 37.2 degrees, a digital device may indicate a basal body temperature of, for example, 37.24 or 37.29. In addition, the acoustic end of measurement indicator will simplify the procedure.
Alternatively, you can opt for a digital basal thermometer , which is a device specifically created to measure TB . Basal thermometers are often associated with specific apps, which allow you to store measurements, keep track of all data and report which days are fertile.
Naturally, these devices have very different prices. The most sophisticated can even cost a few hundred euros.
On the other hand, forehead infrared thermometers (to be brought close to the forehead) or earphones (to be inserted into the ear), which are often used to measure children’s fever, are NOT suitable .
2) Always use the same thermometer and the same method
The thermometer used must always be the same, as well as the measurement method. This means that if you decide to take your temperature vaginally , you will have to continue in this way. But where is the basal body temperature preferably measured ? And how long should you keep the thermometer ?
Rectal measurement
The rectal route is the most accurate method of measuring basal body temperature . Here’s how:
- lie on your side with knees bent;
- insert the bulb of the thermometer into the rectum;
- keep it 5 minutes if using a regular thermometer or until the beep if using a digital thermometer.
Vaginal measurement
Vaginal measurement is almost as accurate as rectal measurement . To take your vaginal basal temperature:
- lie on your back with your legs open or closed;
- insert the bulb of the thermometer into the vagina;
- wait 5 minutes if using a regular thermometer or until the beep if using a digital thermometer.
ATTENTION to the position of the legs , which must always be kept in the same way . Measurements can give very different results with legs open or legs closed.
Oral measurement
This type of measurement is less accurate than the previous ones. Also, oral basal temperature will be slightly lower than rectal. In any case, the trend and not the absolute temperature value is important to analyze the graph. To take basal body temperature by mouth:
- take a comfortable position;
- insert the bulb of the thermometer under the tongue, always on the same side and close to the molars (heat pocket);
- keep your mouth closed and breathe through your nose;
- wait about 8 minutes if using a regular thermometer or until the beep if using a digital thermometer.
Underarm measurement
Taking axillary basal temperature is not recommended and is of no use to this method.
3) Keep the thermometer on your bedside table
Basal temperature is measured upon waking up, before getting out of bed. For this, it is important to keep the thermometer in a place where it is easily accessible.
If you don’t use a digital thermometer, make sure the thermometer is below 36° before falling asleep , so you don’t have to shake it (and therefore move) before taking the temperature.
4) Measure the tb every morning, immediately after opening the eyes
Taking your basal temperature should be the first thing you do in the morning as soon as you open your eyes. If you get up by mistake, don’t mark it on the graph because it will no longer be reliable.
The banal physical activity of getting out of bed causes the body temperature to change. Having to analyze changes of tenths of a degree , even small variations can compromise the readability and therefore the interpretation of the graphs.
5) Measure your tb before 8am
it is important to always take the temperature before 8 in the morning . This is because basal temperature measured after 8 o’clock may be higher .
It is not necessary for the measurement to always take place at the same time, but a variation of up to an hour and a half is permitted .
If you take your temperature after 8 or more than an hour and a half apart, it’s important to note it in the notes.
4) Mark on the graph if you didn’t sleep during the night
Basal temperature should always be measured after at least 3-4 hours of continuous sleep (some say 6 hours) . If you don’t sleep regularly at night and get up often, your temperature when you wake up may be altered.
Other factors that can compromise correct measurement are:
- going to bed later than usual . If you go to bed after midnight, your morning temperature can be altered;
- late dinner ;
- excessive consumption of alcohol the previous evening;
- ailments of various kinds;
- some medications .
These occurrences must be reported on the graph, for a correct interpretation. Furthermore, it is also useful to mark the symptoms, the dates of intercourse and the results of any ovulation sticks , to have a more complete picture.
6) If you have your period, you can wait for the flow to end
If you wish, however, you can continue to measure your TB even during your period , so you don’t break the habit.
7) For those who work shifts
In this case, graphs can be created that can be interpreted only if the basal temperature is always measured at the same time , during the day or in the evening. Before the measurement, try to rest at least an hour or so in a sitting or lying position. Alternatively, you can take your temperature after an afternoon nap.
Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.
Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.