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The Sympto-Thermal Method
Author: Stella Kitchen

A multi-indexed method of Natural Family Planning. The Sympto-Thermal Method (STM)* charts the primary signs of fertility (cervical mucus & Basal BodyTemperature) as well as the secondary signs of fertility (cervical changes, breast tenderness, etc.). This method is based on the work of various scientists, including Billings, Doering, Keefe, Prem, Roetzer, and Vollman.

The careful observation and charting of the several signs of fertility on a day to day basis by couples will ensure success in achieving their family planning goal. When practiced each day, this observation will soon become part of a woman's normal daily hygiene.

Key Words: Cervical Mucus BBT Daily Observation

*For further information see: John Kippley's The Art of Natural Family Planning. (Cincinnati, OH: Couple to Couple League, 1996).

The Basal Body Temperature (BBT) is the waking temperature of a woman's body after she has had at least six hours of sleep. The role of the BBT in this method is to support and confirm the mucus sign and identify that ovulation has taken place. The BBT is taken at approximately the same time each day under the same conditions. During the pre-ovulatory phase it remains at a low level. It is only after ovulation has taken place that a significant rise in the temperature can be seen (see figure 3).

The beginning of the cervical mucus symptom is the beginning of the potentially fertile phase. In the pre-ovulatory phase, the increase in estrogen levels affect cervical mucus. As estrogen increases the cervical crypts are stimulated to produce mucus that is thin, clear, and lubricative. A woman will feel wet when estrogen levels increase. As cervical mucus gradually changes it will become clear in appearance and sometimes even blood tinged; stretchy when picked up and held between two fingers; and will have the sensation of slipperiness, lubrication, and/or wetness. Peak day is the last day of this type of mucus. Ovulation will occur on or around Peak, after which the mucus changes back to a thicker and sticky texture (see figure 2).

Additional signs during ovulation include: cervical changes; breast sensitivity; lymph node swelling in the groin; abdominal pain; and/or swelling of the vulva. When the presence of fertility signs are recorded on a chart, these secondary signs should also be noted and used to determine the event of ovulation.

As a direct result of ovulation the hormone progesterone is produced by the body and changes the characteristics of the cervical mucus, making it thick and sticky. The woman's body temperature also rises as a result of progesterone, and this change can be seen in the daily taking of the BBT. As described above, the first days of the BBT will be low (pre-ovulatory phase). A shift of about .4 F will occur after ovulation. The couple should observe six low temperatures prior to the Peak day. After Peak day, three high temperatures are recorded. The post-ovulatory (infertile) phase of the cycle is counted from the third high temperature after Peak until the onset of the next menses (the beginning of a new cycle). The post-ovulatory phase will last 10-16 days.

Achieving Pregnancy
The optimum time to achieve a pregnancy is from the onset of mucus until Peak day. The fertile phase continues until the woman experiences the third high temperature. A high temperature level sustained for 18-20 days past Peak day, confirms that conception has taken place. Knowing the exact time of conception assists physicians in determining the due date of the baby rather than guessing based on ambiguous data.

Avoiding Pregnancy
During the pre-ovulatory phase of the cycle, a woman must watch for the presence of cervical mucus. Days of dryness may be considered infertile and intercourse could take place in the evening of alternate nights. Alternate nights are used to ensure that any seminal fluid from the previous night's intercourse has not masked the onset of cervical mucus.

If pregnancy is to be avoided, a couple should stop having intercourse or genital to genital contact as soon as mucus is observed or a sensation of moistness is felt. Peak day is identified as the last day of the most fertile sign, whether it is the last day of slippery, stretchy or blood tinged mucus or the last day of a lubricative, wet sensation. Peak day cannot be reliably identified until the following day, when mucus undergoes a change due to the influence of progesterone.

The Sympto-Thermal Method emphasizes the relationship between BBT and the presence of mucus (see figure 2). Therefore, it is very important to make accurate observations, record them carefully, identify Peak day correctly, and confirm the beginning of the infertile time by a rising temperature pattern. When these signs have been confirmed, the infertile phase of the cycle begins and intercourse is again available.


Stella Kitchen, Director of Natural Family Planning, Catholic Diocese of Harrisburg, PA. Stella has taught NFP for over fifteen years and is a trainer of teachers. Stella is a member of the NFP National Advisory Board to the Diocesan Development Program for NFP. She and her husband Roger have made NFP a vital part of their twenty-five year marriage.