What is the basal body temperature method and how is it performed?

By (embryologist) and .
Last Update: 01/31/2023

When a couple is seeking pregnancy, there are several methods to try to increase the chances of getting pregnant. All of them are based on estimating when ovulation will occur in order to calculate the woman's fertile days.

One such method is basal body temperature. In women, basal temperature varies slightly depending on the time of the menstrual cycle. Therefore, this method is based on detecting this physiological change in the woman's basal temperature, which will help determine when ovulation has occurred.

Therefore, it is a traditional, natural, economical method that can be easily performed at home. However, this method can be cumbersome to perform (it requires commitment to measure basal temperature daily) and has some drawbacks.

What is the basal temperature method?

Basal temperature is our body temperature at rest. Therefore, the basal temperature is measured immediately after waking up, without getting out of bed, so as not to perform any type of activity or effort before the measurement that could alter the result.

If a daily basal temperature record is made from the beginning of the menstrual cycle (the first day of menstruation), the woman will observe a 0.3-0.5°C increase in her basal temperature, which occurs after ovulation.

The explanation is that, once ovulation occurs, the remains of the empty follicle in the ovary give rise to the corpus luteum. The corpus luteum produces estrogens, but especially progesterone, which is responsible for the increase in basal temperature.

In this way, after several menstrual cycles by recording the temperature daily, the woman will be able to find a pattern that will allow her to estimate when ovulation will occur.

Ovulation is the release of an egg from the ovary to be picked up by the fallopian tubes, where a sperm could fertilize it.

At this point, it is important to know that a woman's most fertile days correspond to the day of ovulation, the 3-5 days before (because sperm can survive 3-5 days in the woman's reproductive tract waiting for the egg) and the day after (because the egg only survives 12-24 hours after ovulation).

How to measure basal temperature correctly?

To apply the basal temperature method correctly and to try to be as accurate as possible, it is convenient to take into account these recommendations:

  • Basal temperature is ideally measured orally, vaginally or rectally. Once the route has been chosen, the basal temperature should be measured every day at the same site (at least during that menstrual cycle) to avoid any variation.
  • The thermometer should be at hand, ready on the bedside table, and the same thermometer should always be used.
  • Basal temperature measurement should be the first thing to be done every day after waking up, without any kind of activity beforehand.
  • It is important to always measure the basal temperature at the same time.
  • The woman should be relaxed during the measurement, at rest, without any movement or talking.
  • Once the daily measurement has been taken, the basal temperature should be recorded on a graph as follows.

For all these reasons, the basal body temperature method requires commitment and perseverance on the part of the woman.

Factors that can affect basal temperature

In addition to the above tips, it is important to keep in mind that certain factors can affect basal temperature. Among these factors we can mention the following:

  • Illness and/or fever.
  • Lack of rest: not having slept well, staying up late, staying up late. The temperature measurement is more accurate if you have had a long period of sleep.
  • Stress.
  • Drinking alcohol
  • Some medications.

The woman should note any factors that may have altered her basal temperature, as these may produce variations in temperature that do not correspond to ovulation. Therefore, these factors should be taken into account when interpreting the basal temperature graph.

Interpret the basal temperature graph

If the woman wishes to follow the basal temperature method, she should measure and record her basal temperature daily on a chart. To do this, you should start recording your basal temperature on the first day of menstruation, i.e. day 1 of the menstrual cycle.

To elaborate such a graph, the ideal is to use a grid sheet and place the temperature on the vertical axis (a range of 35.5 to 37.5°C) and on the horizontal axis each of the days of the cycle. However, you can find templates that already have this graphic drawn and even mobile applications, which makes it much easier to carry out this method.

If a paper chart is used, each day the basal temperature will be noted with a dot, according to the day of the menstrual cycle in which the woman is and at the height of the temperature obtained in the measurement. At the end of the menstrual cycle, all the dots will be joined to form a line to see more clearly the increase in basal temperature.

Basal temperature rises 0.3-0.5°C after ovulation, in the luteal phase luteal of the menstrual cycle, in response to the increase in progesterone. Therefore, if the woman is able to establish a pattern after several menstrual cycles using this method, she will be able to estimate which day the increase will occur. Thus, if you are looking for pregnancy, you can have sex in the previous days, which will be when you are more likely to get pregnant because they are the fertile days.

If the woman does not become pregnant, progesterone levels will drop, as will basal temperature. This will occur just before menstruation (the start of a new menstrual cycle), which means that the basal temperature will remain elevated until the next period arrives.

On the other hand, if the woman becomes pregnant in that menstrual cycle, progesterone levels will not drop and the temperature will remain elevated.

Advantages and disadvantages

Among the advantages of the basal temperature method for the observation of fertility we can highlight that it is a method:

  • Natural.
  • Simple.
  • Economic.
  • No risks or side or adverse effects.

In addition, the basal temperature method allows a woman to better understand her menstrual cycle and the changes occurring in her body.

However, among its main disadvantages is that a woman will detect the increase in basal temperature when she has already ovulated, so her most fertile days will have already passed.

Therefore, it will be necessary to record the basal temperature during several menstrual cycles, until a pattern is found that allows estimating the day that ovulation will occur and the fertile days, to know when pregnancy is more likely to occur. However, this requires regular menstrual cycles.

Another possible disadvantage is that this method can be somewhat tedious to carry out, as it requires a lot of perseverance. On the other hand, the basal temperature method can be ineffective and inaccurate, so it would be advisable to perform it together with other methods such as the observation of the appearance of the cervical mucus or the use of ovulation tests.

In the following article you can read much more information about all these methods: What are the signs of fertility in women?

FAQs from users

Can the basal temperature method be used as a contraceptive?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

The basal body temperature method could be used as a contraceptive if unprotected sexual intercourse is avoided from the time of menstruation until 3-4 days after the basal body temperature has risen. Among its advantages is that it is a natural, simple and inexpensive method. However, it is a method that is not very effective as a contraceptive, which may make its use inadvisable.

Finally, it is important to mention that the basal temperature method as a contraceptive does not protect against sexually transmitted diseases (STDs).

Can the basal temperature method confirm if I am pregnant?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

The basal body temperature method can only make a woman suspect that she may be pregnant if menstruation does not come on the expected day and the basal body temperature remains elevated and does not drop.

Therefore, if after having estimated the day of ovulation, the basal body temperature remains elevated for a period of 18 days or more, it is possible that the woman is pregnant and a urine or blood pregnancy test should be performed to confirm this.

What is the basal temperature before ovulation?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Generally speaking, the basal temperature before ovulation occurs can be around 35.5-36.7°C.

However, due to the physiological changes that take place in a woman's body throughout the menstrual cycle, once ovulation has occurred the basal temperature will rise by 0.3-0.5°C, due to the hormone progesterone.

Suggested for you

If you want to know more about the cervical mucus method, you can access the following link: How is the cervical mucus during ovulation and fertile days?

If, on the other hand, you wish to have more information about ovulation tests, we recommend you to visit this article: Ovulation test: how does it work and what are they for?

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FAQs from users: 'Can the basal temperature method be used as a contraceptive?', 'Can the basal temperature method confirm if I am pregnant?' and 'What is the basal temperature before ovulation?'.

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 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-CV
Adapted into english by:

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