Simplified rules for women experienced in using NFP methods
To determine fertile and infertile days, women who are experienced in using Natural Family Planning (NFP) or Fertility Awareness Methods (FAM) may follow a simplified procedure, which can significantly reduce the time required for observation without compromising the effectiveness of the method.
- A woman may use this simplified approach if she has been conducting systematic fertility observations and has completed at least 12-24 cycle charts.
- To determine the preovulatory infertile period, one of the following rules may be applied: the modified Döring rule, the “W” rule, or the Rötzer rule.
- Basal body temperature measurements may begin with the appearance of cervical mucus and should be continued until the fourth day of elevated temperature.
- The postovulatory infertile phase begins on the evening of the third consecutive day of elevated basal body temperature at the higher-temperature level.
Physiology of fertility
Maturation of woman
Avoiding conception
Pregnancy planning
Fertility after childbirth
Fertility problems
Premenopause and menopause
Through daily observation of your body over the past 12–24 cycles, you have already gained practical skills and valuable experience. You are familiar with the typical length and pattern of your cycles, as well as your usual lower and higher temperature levels. As a result, you can adopt more flexible assumptions and apply a shortened and simplified observation procedure.
Principles of simplified observation
- Begin measuring basal body temperature (BBT) when you first observe the appearance of cervical mucus or notice a change in your usual secretion.
- Continue BBT measurements until the fourth elevated temperature, taken immediately after waking, following the mucus Peak Day. It is essential to be familiar with your individual lower- and higher-temperature levels.
- Typically, menstruation occurs 10-15 days after the mucus Peak Day or 10-14 days after the first elevated temperature, as the length of the luteal phase is generally stable for each woman.
To determine the end of the preovulatory infertile phase, you may apply one of the following rules:
- modified Döring rule (Pearl Index < 0.2);
- Rötzer rule, based on long-term cycle chart observations, which allows the first six days of the cycle to be considered infertile (PI < 0.2);
- computational (clinical) rule;
- “W” rule, which assumes that all days before the appearance of the “W” sensation (a pronounced sensation of moisture in the vaginal vestibule indicating detailed observation) are preovulatory infertile days (PI ≈ 0.9);
- cervix rule, in which a hard, closed, and low cervix indicates infertility, while a soft, open, and high cervix is a sign of fertility (PI ≈ 0.9).
The postovulatory infertile phase (absolute infertility) begins on the evening of the third consecutive day of elevated basal body temperature, provided that the mucus Peak Day has been observed.