What is the Sympto-Thermal Method?


The Sympto-Thermal Method (STM) is an effective, co-operative, scientifically-based and inexpensive method of natural family planning. The Sympto-Thermal method is based on awareness of a woman's natural cycle of fertility, and the knowledge of the man's constant fertility. This enables a couple to understand, accept, and use their shared fertility in making choices about planning their family.

The Sympto-Thermal Method is the most trustworthy of all natural family planning methods because it incorporates several signs of the woman’s fertility: cervical mucus, cervix changes, morning temperature, and calculation to determine the beginning and the end of the fertile period.

The Menstrual Cycle…unlock the secrets of your fertility!

The menstrual cycle is divided into three phases with ovulation being the main event.  Before ovulation it is called the pre-ovulatory phase or relatively infertile phase and after ovulation the post-ovulatory phase or definitely infertile phase.

  • the pre-ovulatory phase or relatively infertile phase
  • the ovulatory phase or probably fertile phase
  • and the post-ovulatory phase or definitely infertile phase 

The Pre-ovulatory Phase

The pre-ovulatory phase begins on the day the menstrual flow starts. It is variable in length.

What happens in this phase?

In this first phase, the woman’s body prepares itself for ovulation. In the ovaries, a few primitive ova start to develop. Throughout the growing process, the follicle surrounding the developing ovum produces a hormone called estrogen. As ovulation approaches, estrogen acts on the whole body system causing cyclical changes. Conditions change to become favourable to the survival and transportation of the deposited sperm:

  • the cervical mucus becomes wet and more lubricated
  • the cervix becomes softer and more open
  • the lining of the uterus (the endometrium) thickens to potentially receive a fertilized egg

The length of this first phase varies. Ovulation occurs sooner or later depending on conditions within a woman’s lifestyle: stress, season, emotions, nutrition and health. It is the variation of this phase that determines the woman’s cycle length (see figure below).


Ovulation occurs after estrogen reaches its peak level. The pituitary within the brain center secretes a hormone that triggers ovulation. The follicle then bursts open and releases the ovum which is picked up by the fringes of the fallopian tube, and is guided into it. At ovulation, the presence or absence of sperm cells determines the fate of the released ovum. The ovum will live for a maximum of 24 hours (averaging between 8 and 12 hours). Occasionally, a second ovulation may occur a few hours after the first one; however, both ova will disappear within the 24 hour ovulation window, if not fertilized. If the ova are fertilized by separate sperm cells, non-identical twins are conceived.

The Post-ovulatory Phase

The post-ovulatory phase begins after ovulation and ends on the last day of the cycle (the day before menstruation begins again). It is constant in length for the same woman.

After ovulation has occurred, the follicle transforms into the corpus luteum, which releases a hormone called progesterone into the woman’s bloodstream. The body is then ready to protect the potentially fertilized egg. At this stage, the presence of progesterone in the body makes the cervix firmer and the cervical opening smaller. Cervical mucus thickens and forms a kind of gelatinous plug which protects the uterus from outside elements. Progesterone also causes the lining of the uterus to build up in preparation in the event of implantation of a developing baby.

For the next 12 to 16 days, two scenarios are possible:

  • For one week, progesterone is released into the bloodstream. If fertilization and implantation have taken place, the production of progesterone increases, and plays a determinant role in sustaining pregnancy.
  • Or, for one week, progesterone is released into the bloodstream. If there is no pregnancy, the release of progesterone slows as the corpus luteum degenerates, and then the lining of the uterus will shed during the next menstruation.

How Does the STM Work?  Putting it all together…

The Sympto-Thermal Method works by recording daily observations of the woman’s fertility:

  • the woman's basal body temperature
  • cervical mucus
  • changes in the cervix
  • and other symptoms of ovulation


These observations are made and then recorded on special Serena Sympto-Thermal Method charts. By charting all the signs of the woman’s fertility, the information gathered can be used to empower couples to make choices to postpone or engage in intercourse, according to their wish to achieve or avoid pregnancy.

The STM can also be used throughout a woman’s reproductive lifespan, including various situations such as breastfeeding and pre-menopause. However, the rules of the method vary in these special situations. So couples should consult a Serena teacher-couple to learn the rules applicable to their special situation.


Using the Sympto-Thermal Method means charting.  All of the signs of fertility (temperature, mucus, cervix, other…) are recorded on special charts.  With teaching from a certified Serena teacher-couple, couples will learn how to chart the signs of fertility and then interpret this information in order to identify the relatively infertile, fertile, and infertile phases of the menstrual cycle.

How can Charting help you?

By recording information about each menstrual cycle on a chart, and having received instruction from a certified Serena teacher-couple in the Sympto-Thermal Method, it is relatively easy to:

  • discern the period of ovulation
  • identify the period of natural infertility
  • predict the onset of menstruation
  • follow each cycle as it unfolds
  • discover menstrual irregularities
  • detect possible causes of infertility
  • observe the re-establishment of ovulatory cycles after oral contraceptive use, breastfeeding or pregnancy
  • confirm early pregnancy
  • recognize the approach of menopause



The use-effectiveness of the Sympto-Thermal Method is dependent on how motivated the couple is to constantly and carefully follow all the method's rules. For the most satisfactory and effective experience with the Sympto-Thermal Method, we strongly encourage couples to meet with and be instructed by a qualified accredited Serena Canada teacher-couple. This is the best way to benefit from accurate knowledge and instruction in the application of the method.

Note: The STM does not protect against sexually transmitted diseases or infections.

The information contained on this website is not enough to be able to practice the STM nor is it intended to substitute for proper instruction from a certified teacher couple.


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