The Symptothermal Method is an effective, co-operative, scientifically-based and inexpensive method of Natural Family Planning. It is based on the awareness of the fertility of the couple.

How The Symptothermal Method Works

The Symptothermal Method works by recording and interpreting daily observations of the woman’s fertility:

  • Basal Body Temperature
  • Cervical Mucus
  • changes in the Cervix
  • other signs of Ovulation

This knowledge enables couples to decide to postpone or engage in intercourse, according to their wish to achieve or avoid pregnancy.

The Symptothermal Method can be used throughout a woman’s entire reproductive lifespan, including during breastfeeding and Perimenopause. The rules of the method vary in these special situations so couples should consult a Serena teacher-couple to learn how the method is used in their particular situation.

Why The Symptothermal Method Works

The Menstrual Cycle is divided into three phases.

Pre-Ovulatory                                   Ovulation                Post-Ovulatory

The Pre-ovulatory phase is variable in length beginning the day the menstrual flow starts. During this phase, the woman’s body prepares for ovulation. In the ovaries ova start developing and the follicle surrounding each ovum start to producing estrogen. As ovulation approaches, estrogen causes changes in the body to encourage the survival and transportation of sperm:

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

The timing of ovulation varies depending on many factors: stress, emotions, nutrition and health. The variation in the length of this pre-ovulatory phase determines the woman’s overall cycle length.

After estrogen reaches its peak level, the pituitary gland secretes luteinizing hormone(LH) which triggers ovulation. The follicle releases the ovum which is picked up by the frimbrae of the fallopian tube.  At ovulation, the presence or absence of sperm determines the fate of the released ovum.  The ovum will live 8 to 12 hours on average.  Occasionally, a second ovulation may occur a few hours after the first one (This is the cause of non-identical twins).  Even if there is a double ovulation, once the first ovulation takes place there is only a 24-hour window each cycle during which an ovum may be fertilized.

The post-ovulatory phase begins after ovulation and ends the day before the next Menstruation.  Unlike the pre-ovulatory phase, the length of this phase does not vary from cycle to cycle.  After ovulation, the follicle transforms into the corpus luteum which starts releasing progesterone to prepare the body to protect a potentially fertilized egg. This causes the cervix to become firmer and closed.  The cervical mucus thickens forming a plug, protecting the uterus from foreign bodies, and the basal body temperature slightly rises. Progesterone also causes the lining of the uterus to thicken in preparation for implantation.

After one week:

  • If fertilization and implantation have taken place, the progesterone level will continue to increase to sustain the pregnancy.
  • If there is no pregnancy, over the following week the release of progesterone slows as the corpus luteum degenerates leading to menstruation

This information reveals key reasons why the Symptothermal Method works.

  1. There are observable changes to the woman’s body throughout the menstrual cycle.
  2. Each cycle there is only one small window of time during which a sperm could fertilize an egg.

In each cycle, there is a window of time during which a woman is fertile, and this can be identified by observing the changes in her body caused by estrogen and progesterone.  Intercourse during this fertile window could lead to pregnancy. Intercourse outside of the fertile window will not.


By receiving instruction from a certified Serena teacher-couple in the Symptothermal Method and recording information about each menstrual cycle, couples can easily:

  • discern the time of peak fertility
  • identify the phases of natural infertility
  • predict the onset of menstruation
  • discover menstrual irregularities and detect possible causes of infertility
  • observe the return of fertility after hormonal contraceptive use, breastfeeding or pregnancy
  • confirm early pregnancy
  • recognize the approach of Menopause


Serena teaches the Symptothermal Method of natural family planning. When taught properly and used consistently, a couple has a greater than 99% chance to postpone pregnancy. (See Effectiveness of the Symptothermal Method for more details.) For the most satisfactory and effective experience with the Symptothermal Method, we strongly encourage couples to be taught by a certified teacher-couple. This is the best way to benefit from accurate knowledge and instruction in the application of the method.

The Symptothermal Method is such a robust natural family planning method because it incorporates several signs of the woman’s fertility: cervical mucus, cervix changes, and basal body temperature.These three signs are used to help identify the beginning and end of the fertile window.

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