How to determine fertile and infertile days when you are inexperienced in NFP?

Determination of the fertile and infertile days during the menstrual cycle should not be a big problem for any woman. This ability, however, requires understanding the changes that occur in female body during the menstrual cycle and determination in carrying out and recording your daily observations. Acquiring this skill gives a woman a number of benefits: allows her to understand her own body and emotional changes much better, and, what’s more important, it gives her the confidence in many life situations - particularly intimate ones.

If this is your first contact with the natural methods of fertility recognition or you have just started to carry out your self-observations (1-12 Cycle Cards), you should adopt a bit more conservative assumptions to determine the fertile and infertile periods:

  • In the case of women who are inexperienced in conducting self-observation, the infertile days should not be determined at beginning of the cycle, but only postovulatory infertile period.
  • Postovulatory infertile period includes the time from the end of the ovum life and the formation of the corpus luteum to the next menstrual period. Conception of a child is  impossible. This is a phase of  absolute, that is certain infertility, with the Pearl index (PI) = 0
  • It can be assumed that the postovulatory infertile period begins in the evening of the third day of basal body temperature increase to higher temperatures level.

Rules for the women who aren’t experienced in their bodies self-observation and recognizing of fertility symptoms, are more restrictive than for the other women. They determine a period of about 12 cycles as necessary to learn everyday observations, personal course of the cycle and rhythm of their own fertility, and above all, to apply the rules of determining the fertile and infertile days.

If you have just started to observe the natural signs of fertility (so-called biomarkers of fertility), you should not determine any infertile days at the beginning of the cycle (preovulatory phase), and if you’re trying to avoid pregnancy, you can have intercourse only during the postovulatory infertility phase.

Even after the first cycle of observation you will notice how your symptoms of fertility are changing and what your basal body temperature chart is. After this phase of observations you will be able to use your notes concerning the length of previous cycles.


How to determine the infertile days of preovulatory phase?

The only rule used to determine relative fertility days at the beginning of the cycle which is applicable for  the women who are inexperienced in observations is the calculation rule.


Infertile days before ovulation, calculating rule based on the shortest menstrual cycle

  • If your previously observed cycles weren’t shorter than 26 days, then determine the end of your preovulatory infertility in the evening of the sixth day of the cycle (assuming that during that day you haven’t observed any mucus symptom or permanent change of secretion).
  • If your cycles were shorter than 26 days, then subtract 20 days from your shortest cycle. As a result, you get the number of infertile days at the beginning of the cycle.
  • However, if your menstrual period has occurred every three weeks, then you should not regard any days at the beginning of the cycle as infertile ones.


How to identify fertile days?

Each day when you can observe some mucus secretion or some change in your constant secretion, or you have the feeling of moisture or wetness, means the day of your possible fertility.

It should be noted that not every bleeding is menstrual one. Many women have mid-cycle bleeding during the periovulatory phase. It is also a fertile time, especially when preceded by the presence of mucus and occurs in low temperatures phase.

If you have a series of cycle observation cards, you can easily distinguish those bleedings from the actual menstruation. Bleeding may be considered as menstruation only if it is preceded by several days (at least three days) of the higher temperatures phase. If it occurs during the  lower temperatures phase it should be regarded as  a mid-cycle bleeding, and its last day should be regarded as the peak of mucus day and marked with “●” (unless after this date there is some mucus secretion).

The period of fertility falls on 6-7 days during the lower temperatures phase and  1-2 days during the higher temperatures phase providing that there is mucus secretion of the cervix, which allows the sperm to survive in a woman’s reproductive tract until ovulation. On average, sperm has the ability to fertilize in favorable conditions for 4 days, but years of researches confirmed the possibility of its survival up to 6 days, that is why this period is


How to determine the infertile days in the postovulatory phase?

The days of absolute (postovulatory) infertility can be determined as follows:

  • first, determine the mucus peak day - the last day of mucus symptoms with the most fertile features,
  • then wait for the next three temperature measurements after waking up, which should be higher than the level of lower temperatures (determined by the highest of the six temperatures preceding the increase). They should aim towards the higher temperatures level (we denoted it automatically 0.2 ˚ C above the level of lower temperatures). If the third of the recorded higher temperatures is at least as high as the higher temperatures level then the evening of that day begins a period of your absolute infertility – physiological one.

If you are accustomed to observing your own fertility, which means having completed at least 12 Cycle Cards, you will be able to use the remaining rules for determining the preovulatory infertility that is the Döring’s rule, the Rötzer’s rule, the “W” rule or the rules for the cervix observation. You will also be able to apply the principles of simplified observations.


See more:

What physiological changes occur in your body during the menstrual cycle?

How can you observe and interpret the signs of fertility using fertility Cycle Card?

What are the specific rules for determining the fertile days and infertile days?

How to use simplified rules for experienced woman?

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