What is the effectiveness of symptothermal natural methods compared to contraceptives?
The effectiveness of a given method is measured using the Pearl Index (PI), developed by Raymond Pearl in 1932. It is calculated as the number of unintended pregnancies divided by the number of observed cycles, multiplied by 1,200. The index indicates how many out of 100 women using a specific method are expected to become pregnant within one year. The lower the Pearl Index, the more effective the method. When no method of pregnancy prevention is used, the Pearl Index is approximately 85.0.
Physiology of fertility
Maturation of woman
Avoiding conception
Pregnancy planning
Fertility after childbirth
Fertility problems
Premenopause and menopause
| Method | Effectiveness | Pearl Index (PI) |
|---|---|---|
| Natural methods – symptothermal (Rötzer method) | 99,8% | PI = 0.2 |
| Natural methods – with imperfect rule adherence by users | 99,2% | PI = 0.8 |
| LAM method – first 12 weeks of exclusive breastfeeding postpartum | 100% | PI = 0.0 |
| LAM method – first 30 weeks of exclusive breastfeeding postpartum | 98% | PI = 2.0 |
| Cycle computers | 99,4% - 99,6% | PI = 0.6-0.4 |
| Male sterilization (vasectomy) | failure rate: 1 in 2,000 | |
| Female sterilization (tubal ligation) | failure rate: 1 in 200 | |
| Combined oral contraceptive pill |
97% - 99,8% (according to J. Guillebaud) |
PI = 0.2-3.0 |
| Hormonal intrauterine devices (IUDs) | 99,2% - 99,4% | PI = 0.6-0.8* |
| Intrauterine devices (IUDs) | 98% - 99,7% | PI = 0.3-2.0* |
| Hormonal implants and injections | 99% - 99,7% | PI = 0.3-1.0* |
| Progestin-only pill (minipill) | 96% - 99,7% | PI = 0.3-4.0* |
| Contraceptive patches | 99,2% - 99,8% | PI = 0.2-0.8 |
| Diaphragm and cervical cap with spermicide | 85% - 97% | PI = 3-15 |
| Male condom | 85% - 98% | PI = 3-15 |
| Emergency contraceptives (used within 72 hours after intercourse) |
2-5% (unintended pregnancies per year of use) |
* The anti-implantation (antinitidational) effect is not included – this means that the data do not reflect the possibility of conception (fertilization of the egg) followed by early miscarriage caused by impaired endometrial function (failure of embryo implantation in the uterine cavity).
** LAM method – Lactational Amenorrhea Method.
Developed based on the following sources:
- Recommendations of the Polish Society of Gynecology on Contraception, Annex No. 2
- Research on the effectiveness of the method by the Institute of Natural Family Planning based on the method of Prof. J. Rötzer
- “Hormonal Contraception” by Dr. Elżbieta Siwiak, INER Scientific Notebooks, Issue No. 3/2005