Basal temperature, what it is, how it is measured, what it is used for

Scientific revision by Antonio La Marca, professor of Gynecology at the University of Modena and Reggio Emilia and director of the Obstetrics and Gynecology Clinic of the Modena Polyclinic

The basal temperature

The basal temperature is still one of the words that women seek on the web when they plan a pregnancy. The measurement of the temperature of the body at rest is a natural methodmainly used in the past, To check the occurrence of ovulation or notthat is, the moment when the mature egg is released by the follicle, being available for fertilization. But – it must be clarified immediately – It is an unconcerted ovulation monitoring systemdue to the many variables that can come into play and that cannot always be controlled. To begin with the variation of body temperature, in addition to hormonal changes (in particular the greater concentration of progesterone) can affect the quantity and quality of sleep, the temperature of the bedroom, the digestion of food, the moods, the consumption of alcohol, the influence, the presence of infections, the intake of drugs.

Once, before the invention of the contraceptive pill, This natural technique was also used with the aim of avoiding unwanted pregnancies But studies have shown that it is unreliable. Before understanding why it is ineffective as a contraceptive tool and in what way could help the woman to have a greater awareness of her ovarian cycle, let’s explain what is meant by basal temperature and how it is measured.

What is it

It is the lowest temperature of our body recorded at rest as soon as we wake up in the morningbefore starting any physical activity. Already at the end of the nineteenth century it was discovered that in fertile women the basal body temperature varies during the month of a few tenths because of the hormonal fluctuations that mark the menstrual cycle (in particular, due to the effect of progesterone). In the prenovulatory phase (the period between the end of menstruation and ovulation) The temperature is less high (the lowest peak can be reached about a day before the start of ovulation) and is between 36.1 and 36.7 degrees on average. While it tends slightly to get up, of about 0.3 degrees, after ovulation (which in a regular cycle of 28 days takes place around the 14th day before the start of the next menstrual cycle) in coincidence with the peak of progesterone in the circle, which acts on the hypothalamus (the brain structure that regulates the body’s temperature) making the body temperature grow. In the luteal phase (the period that follows ovulation, in which the follicle that broke and released the oocyte turns into the luteum body), in fact, it is easier to experience sensations of heat and sweating. The slight increase in the basal temperature continues until about one to two days before the start of menstruation. After that, with the progressive reduction of progesterone levels, the internal temperature returns to descend by realizing the prenovulatory value.

How to measure it

Basal body temperature can be test using a simple digital thermometer (axillary, oral or rectal), of those who normally use to measure the fever (the important thing is that the decimals also detect). Or on the market there are special devices that detect the intravaginal temperature (and in other parts of the body) to determine ovulation. To correctly collect the basal temperature it is necessary that the measurements are performed every dayonce a day, For at least a month (Better, however, try for two to three consecutive months to highlight the oscillation), at the same time, immediately after awakening and preferably before getting out of bed and taking food and drinks. Values ​​can be recorded on specific graphics (which can be downloaded online) or dedicated apps for smartphones.

What can be used for

The observation of an increase in basal temperature does not identify the beginning of the « fertile window » (conception can take place even if there have been unprotected relationships in the two days preceding ovulation since the spermatozoa are vital up to five days) but could confirm the ovulation Or, when basal values ​​lower, report the end of the monthly « fertile window » (which lasts five days). The measurements of the basal temperature, therefore, can help women who want to conceive by monitoring the cycle, to program more targeted sexual intercourse with the partner. But since there are many factors that influence the basal body temperature, to have a more reliable estimate of ovulation, it is recommended to also control the peak of luteinizing hormone in the urine (through a test for home use) and the loss of whitish cervical mucus.

A modest rise in body temperature, in association with menstrual delay, could indicate the beginning of a pregnancy, characterized by the constant growth of progesterone levels (the hormone serves to prepare the uterus to welcome the fetus and to continue gestation).

The limits of the method

The accuracy in the correct detection of ovulation is low. In addition to the reasons described above, also because menstrual cycles could occur without ovulation (called anovulator), in which there is no increase in progesterone and therefore not even of basal body temperature. Furthermore, ovulatory cycles have been documented in which there is no increase in the basal temperature, which could indicate a lack of sensitivity to the action of progesterone by the hypothalamus.

Another thing to know is that The basal temperature technique cannot be considered reliable to protect itself from unwanted pregnancies. If it is true that ovulation takes place on a single day and the oocyte remains suitable for fertilization for about 12-24 hours, it must be equally considered that you can get pregnant even when you have unprotected relationships in the two days preceding ovulation, since the seminal liquid issued in the vaginal channel can survive up to five days.

However, even if the basal temperature measurement method is not perfect for monitoring ovulation, if the woman does not find an oscillation of the internal temperature, a visit to the gynecologist is suggested to investigate any ovulation disorders. In these cases, an ultrasound monitoring of ovulation over the month and the dosage of progesterone must be performed.