An independent US study published in 2016 by FACTS confirms sympto's superiority : 

One day after ovulation (identified by echography) the totally infertile phase begins and lasts until the next menstruation. According to Rötzer’s studies, the Pearl-Index is therefore 0.0: better than any 'pill' provided that the cross-checking of temperature rise and Peak day have been accomplished. According to Rötzer's studies, during the first 5 pre-ovulatory days, the Pearl index is 0.2. For women who have more pre-ovulatory days after day 5, the Pearl index is 0.8 which still compares to the best synthetic contraception. From this angle, there is not straightforward answer to the question of contraceptive effectiveness. This methodological effectiveness depends on the couple's competence to observe abstinence during the fertile days, or to use barrier methods properly, and most importantly on the woman's observation skill.

The overall contraceptive effectiveness of the STM is indicated by a Pearl index of 0.5 according to the standard reader 'Gynäkologie und Geburtshilfe', B. Uhl, 3rd edition, 2006, page 474 (Thieme Verlag).

The English press release of the comparative study of 2013 is available here.

The 2014 study, published in a Swiss gynecological journal, is available here: info@gynäkologie, 4, 2015, 33- 35:
Welche Apps sind für die Verhütung geeignet?

Full Comparative App-Study 2013, only in French

Full Comparative App-Study of 2014


The study of 2013 was published in The European Journal of Contraception and Reproductive Health, Vol. 19, Supplement 1, May 2014, p. 201.

The effectiveness of the system depends on a number of factors:


A) Theoretical and practical effectiveness (called methodological effectiveness) of the classic, manual STM: See the studies list below.

B) Theoretical effectiveness of the symptom engine. sympto has not only integrated the symptothermal laws that have been verified through more than hundred thousands of cycles over the last 20 years. In addition, it has synthesized these rules in a new way (see the Complete Symptothermal Manual). As for comprehensiveness, sympto has integrated the trickiest and rarest cases. Test cycles are available for those who can document a scientific interest. Ever since 2008 (sympto 2) there has been no unwanted pregnancy in several thousands of cycles. This unique result is also due to the fact that sympto users are provided with guidance by a symptothermal counsellor. However, the effectiveness diminishes drastically if the data entered is a) poorly observed, or b) untrue, or c) if the fertile window is not respected (behavior inconsistent with cycle goal, condom problem, etc.). The user-friendliness of the sympto app has been optimized (see sympto easy page).

On sympto we differentiate between the typical, the perfect and the free or uninitiated sympto use: For the typical use, the user has been followed by a counselor and learned the method properly but the couples takes some risks based on the cycle knowledge. The perfect use of sympto happens when the user has a typical use and, in addition, does not take any contraceptive risks and remains perfectly consistent with the observation goals. This is rarely the case but not needed for the couples' effectiveness of contraception! The (experience based) result is almost 0.0 Pearl-index! There is an ongoing study by SymptoTherm to prove this new situation. We have, third, many free and unknown (and unitiated) users who realize very quickly that her entries where not sufficient: they will drop the method or take a counselor or, in many cases, study the manual and do the whole learning process by their own efforts. We do not have the figures of the initiated use as it is a free or Premium use with any counseling. In French, we have the FB page symptothermie where women motivate themselves for this learning process.

A) below the most recent clinical studies: (The WHO studies of the eighties are completely outdated.)

  1. Here a recent summary of most of the studies:
    Osteopathic Family Physician (2013) 5, 2–8:
    Fertility awareness-based methods of family planning: A review of effectiveness for avoiding pregnancy using SORT, Michael D. Manhart, PhD, Marguerite Duane, MD, MHA, FAAFP, April Lind, MD, Irit Sinai, PhD, Jean Golden-Tevald. From the Couple to Couple League, Cincinnati, OH; Georgetown University, Washington, DC; Park Nicollett Clinic, Maple Grove, MN; and Morningstar Family Health Center, Clinton, NJ.
  2. Frank-Herrmann,P., Heil,J., Gnoth,C. et al (2007) The effectiveness of a fertility awareness based method to avoid pregnancy in relation to a couple's sexual behaviour during the fertile time: a prospective longitudinal study. Hum.Reprod., 22, 1310-1319.
  3. Frank-Herrmann P., Gnoth, C., Baur, S, Strowitzki T, and Freundl, G. Determination of the fertile window: Reproductive competence of women - European cycle databases. Gynecol.Endocrinol. 20(6), 305-312. 2005. Ref Type: Journal (Full)
  4. Frank-Herrmann P., Strowitzki T, Wischmann T, Gnoth, Ch, and Freundl, G. Fertility Awareness in der Hormonsprechstunde - ein Pilotprojekt an der Universität Heidelberg. Forschung für die Frau in einer neuen Welt(Deutsche Ges. für Gynäkologie und Geburtshilfe), PB.11.08. 9-12-2002. Springer. Ref Type: Art Work
  5. Frank-Herrmann,P., Freundl,G., Gnoth,C. et al (1997) Natural family planning with and without barrier method use in the fertile phase: efficacy in relation to sexual behavior: a German prospective long-term study. Adv.Contracept., 13, 179-189
  6. Freundl, G. The effectiveness of NFP, demonstrated on two ongoing studies, the German and the European study. IV. Symposium Internacional sobre Regulacion Natural de la Fertilidad (Asociasion Espanola de Profesores de Planificacion Fam. Nat.), 57-64. 1994. Universidad de Barcelona. Ref Type: Art Work
  7. Freundl,G. (2000) Natürliche Familienplanung und "nicht-hormonale Kontrazeption". Gynäkologe, 33, 679-688.
  8. Freundl,G. (2004) Natürliche Familienplanung. In Bender,H., Diedrich,K., and Künzel,W. (eds), Klinik der Frauenheilkunde und Geburtshilfe. Urban & Fischer, München , Jena, pp. 163-172
  9. Freundl,G. (1998) Kontrazeption per Computer. Hormonmesssystem Persona-- Studienergebnisse in Deutschland. (Contraception per computer. Hormone system persona--results of studies in Germany). Fortschritte Der Medizin, 116, 47-48
  10. Freundl,G., Frank-Herrmann P., Godehardt,E. et al (2003) Die Effektivität von Zyklusmonitoren zur Bestimmung des fertilen Fensters . Geburtshilfe.Frauenheilkd., 63
  11. Freundl,G., Godehardt,E., Kern,P.A. et al (2003) Estimated maximum failure rates of cycle monitors using daily conception probabilities in the menstrual cycle. Hum Reprod., 18, 2628-2633
  12. Freundl,G., Suberg,D., Flynn,A.M. et al. (1984) [Natural family planning (symptothermal method) and objective ovulation parameters--a pilot study] Naturliche Familienplanung (symptothermale Methode) und objektive Ovulationsparameter--eine Pilotstudie. Geburtshilfe. Frauenheilkd., 44, 368-374
  13. Gnoth, Ch, Godehardt, D, Godehardt, E., Frank-Herrmann P., and Freundl, G. Kumulative Schwangerschaftswahrscheinlichkeit in natürlichen Zyklen: eine prospektive Studie. Forschung für die Frau in einer neuen Welt (Deutsche Ges. für Gynäkologie und Geburtshilfe). 9-12-2002. Berlin, Heidelberg, Springer Verlag. Ref Type: Art Work
  14. Raith,E., Frank,P., and Freundl,G. (1999) Raith-Paula,E., Frank-Herrmann P., and Freundl,G. (eds), Natürliche Familienplanung heute mit ausführlicher Darstellung der Zykluscomputer. Springer, Berlin, 1-273
  15. Sottong,U., Bremme,M., and Freundl,G. (1992) Lactational amenorrhoea and lactational anovulation in 109 breastfeeding women. Advances In Contraception, 8, 269-270
  16. Sottong,U., Fortrie,C., Bremme,M. et al (1998) Kontrazeption in der Stillzeit Wie werden natürliche Methoden akzeptiert und angewandt? Sexualmedizin, 20, 244-250
  17. Zinaman,M. and Stevenson,W. (1991) Efficacy of the symptothermal method of natural family planning in lactating women after the return of menses. Am.J.Obstet.Gynecol., 165, 2037-2039
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