How to detect pregnancy on a basal temperature chart

Why measure basal body temperature instead of average body temperature to monitor ovulation?

Monitoring basal body temperature is the simplest, cheapest, and most accessible way to detect ovulation.

Body temperature, not influenced by external factors, can be considered the most accurate and reliable.

It fluctuates throughout the day due to stress, cold, heat, exercise, food consumption, etc., and can be measured at any time of the day. Under these conditions, it is impossible to obtain a temperature measurement not affected by external factors.

Does the Basal Temperature work as a contraceptive method?

It is essential to know that although this method is a practical tool, it is far from being 100% reliable. Any hormonal change, fatigue, illness, fever, taking medication, or stress is likely to cause a temperature change and, therefore, a misinterpretation of the curve. Also, the temperature curve is not practical for people with volatile sleep patterns or frequently take alcohol or progesterone-based medications.

The temperature curve is mainly used to analyze the emotional cycle and identify possible fertility problems when a child cannot be conceived after more than one year (for example, anovulation, some women do not ovulate, or do not ovulate at all cycles).

You have all the information about all the contraceptive options that you can find in Contraceptive methods – Types, Use, and Efficacy

How to detect pregnancy on a basal temperature chart

If the basal body temperature remains elevated for more than 14 days after a jump that indicates ovulation and the period does not occur, it may indicate a pregnancy.

The fertilized egg implants in the endometrium if conception occurs (about 4 to 10 days after ovulation).

This may be indicated by a sharp drop in temperature on the graph since early pregnancy is associated with estrogen release, which reduces BBT.

Basal body temperature after conception can lead to a triphasic pattern on your BBT chart, meaning a third temperature level is indicated.

This is the result of excess progesterone that a pregnant woman’s body produces.

Don’t completely trust these signals. Sometimes basal body temperature during pregnancy can be inaccurate and unpredictable. For greater certainty, take a home pregnancy test.

At what point does your basal temperature drop if you are not pregnant?

If you are not pregnant during this cycle, your BBT should decrease 10-14 days after ovulation, around the time you should start your next period.

Advantages of the basal body temperature method

Increase knowledge of how the female body works.

Disadvantages of the basal body temperature method

The flu with a high fever changes the temperature. It is possible that the flu, or any other disorder or illness, can change the basal temperature causing miscalculations.


There are tests on the market that facilitate the calculation of fertile days based on the above measurements. Some have ovulatory strips that measure the concentration of two hormones in the urine, estradiol and LH, which mutate at different cycle stages. This gives a more reliable statistic of the fertile days.

 Jaume, reader, and partner of, wrote us the following request in an email: “I just had the flu this year, and now I have my wife bedridden with the same disease. We have a debate about where the body temperature is captured more exactly, to really know the fever that one has. I say that the most exact thing is through the rectum and in women the vagina, and she thinks that there is enough with taking it in the armpit. Who has the reason?”.

Body temperature can be measured in different body parts, such as those mentioned by Jaume, and we would also add the mouth. However, it is not precisely the same in each area, and in addition to average temperature, that is, the normal temperature in a healthy person, each person tends to show different values ​​depending on the activity, the day, their metabolism, etc.

That is why a statistical average temperature is established, based on decades with thousands of measurements, as we tell you in the body’s average temperature. In this sense, if until a few years ago, the standard average norm temperature was established at 37ºC, the pattern has varied thanks to various studies downwards. One of them is the one published in the Journal of the American Medical Association, which determined that the normal average for adults is 36.7ºC and not 37ºC.

Later the review Normal Body Temperature: A Systematic Review, which studies subsequent studies on body temperature between 1935 and 2017, concluded that the general average body temperature is 36.5ºC and can vary one degree below and one degree above. Therefore, taking this temperature as a standard, experts establish an approximate range of one degree more to determine when we have a fever and when we do not. That is to say, that 37.6ºC would already be having a tenth of a fever.

The right place to place the thermometer

This is relevant because it is precisely estimated that the temperature can vary up to one degree depending on where we place the thermometer. We believe that we do not have a fever when we have crossed the threshold. In any case, measurement is not the only pattern since we must also consider the symptoms. In addition, the average variation does not usually exceed half a degree.

    Straight: it is the area where we have a more accurate measurement of body temperature so that in one or two minutes, we can have the exact measurement. It is used mainly in babies and young children. In adults, it has the disadvantage of comfort and hygiene.

    Vagina gives good measurements but has the disadvantage of presenting alterations due to ovulation and being an excruciating area. In any case, it is used to measure the basal temperature and calculate the fertility period to increase the chances of fertilizing the egg.

    English: In a similar case is the groin in the case of men, although the testicles can also alter the measurement since they usually have a lower temperature than the body. For this reason, it is necessary to ensure that they do not come into contact with the thermometer.

    Mouth: it is another area where fairly precise measurements are obtained in a short time, although again, it is uncomfortable, and saliva can alter the measurement somewhat as it is not a suitable heat transmitter.

    Armpit: it is the most comfortable measurement and therefore the most used and the most inaccurate; It takes a longer time to determine the temperature and can be one-half to one degree lower than in the rectum.

Infrared thermometers

An alternative that eliminates the debate about the ideal point of probing is the infrared thermometer, a health application of industrial thermometers used to measure temperatures inside machines or materials at very high temperatures. They are based on a probe that captures the emission of energy in the form of infrared rays from matter and interprets it in the form of degrees of temperature.

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