However, the reality does not quite match that concept. Difficulty lies in the fact that it is impossible to pinpoint the moment of rupture the follicle and release an egg. It is well known that ovulation occurs – to 28-day cycle – between 12 th and 16 th day of the cycle (ie, a 5-day period). but the number of days during which fertilization can take place, in fact, comes up to seven, as should be taken into account and those two days, during which the sperm retain their ability to fertilization. Exact designation of menstruation shows, moreover, almost all women of variation of 1-2 days in the duration of the cycle, often even more. This difference in cycle time affect the accuracy of the moment release of an egg. Established. that there exists a close relationship between oocyte maturation and the emergence of the next menstruation.

When the cycle is shorter, ovulation occurs sooner, and when the cycle is longer, ovulation occurs later. Repeated pregnancies, breastfeeding, abortion, severe illness, physical fatigue, nervousness, travel, climate variations can also cause a change in the length of the cycle (and ovulation). Among women aged 35-40 years, the change cycle occurs without any apparent reason. This implies that the definition of productive days in a woman is faced with considerable difficulty. Calendar period of menstruation for Women whose menstruation occurs regularly (cycle of 28 days), it can be assumed that fertilization can not be done during the days immediately following the menstrual period (approximately 7 days) and within days, that precede the next period (after 18 of the 20 th day). Consequently, the period of physiological neoplodotvoryaemosti can be set only in women with regular cycles of 27-29 days.

To this end, Knaus recommends making Calendar of menstruation for at least a year. To determine the fruitful days in the case of variable cycle, you must subtract 19 from the very small numbers, and 12 of the largest numbers. Example A: A cycle in 24-29 days: 24-19 = 5, 12/29 = 17 Fertilization possible from 5 th to 17 th day. Example B: The cycle in 27-30 days: 27-19 = 8 12/30 = 18 fertilization is possible from 8 th to 18 th day.