One of the best known methods of natural family planning is the calendar method. It involves periodic sexual abstinence based on a calculation, as the name suggests, according to the calendar. This method results from the observation of a woman’s monthly cycle and the detailed knowledge of its course and physiology.
The researchers Ogino and Knaus were the first to describe it, hence the name may be associated with the above-mentioned surnames. These researchers found that the second phase of the cycle, called the luteal or corpus luteum phase, usually lasts the same length – about 14 days. What does it mean? Namely, according to researcher Ogino, the release of the egg, or ovulation, occurs about 12 to 16 days before menstruation. Knaus specified this time by saying that ovulation occurs exactly on the 15th day before menstruation. These observations led to the assumption that after taking into account the survival time of the egg and sperm cells, the fertile and infertile period of a woman can be determined. The assumptions are clear. Unfortunately, this method has many limitations that place it at the far end of the ranking of effective methods. First of all: the first phase of the menstrual cycle has a variable duration, which affects the duration of the entire cycle. Secondly, a woman must conduct self-monitoring for several months (minimum 6) to be able to determine the length of her own menstrual cycles. The next step is math. The calendar determination of the beginning of the fertile phase of a woman consists in subtracting the number of 18 days from the shortest cycle, and the determination of the end of this phase by subtracting 11 days from the longest cycle. The range of days calculated in this way makes one abstain from sexual intercourse. Depending on the length of the cycles, the “safe” time is a few days before and after menstruation. Another limitation is irregular menstruation, in which it is difficult to determine the division into the first and second phase of the cycle, when the key point is the release of the egg, i.e. ovulation.
The commonly used Pearl Index, specifying the number of pregnancies per 100 women using a specific method of contraception for 1 year, ranges from 14 to 50 with this method, which proves that every second couple using this method may expect “unplanned ” child.
Text: Katarzyna Kuśmierczyk
Read also about the thermal method