The so-called calendar («rhythm-method») behaves to the number of quite harmless and physiological methods of contraception.
It is known that at a 28-daily cycle ovulation usually takes place on 12 - 14th day. Taking into account that an ovule saves a capacity for the impregnation during 24 hours after ovulation, a «dangerous» period at a 28-daily cycle is on 10 -17-é day. For the calculation of «dangerous» periods there are different tables and methods.
Method 1
Duration of menstrual cycle (it is determined from the 1th day of menstruation to the 1-st day of the following) is divided on 2. The low bound of possible day of ovulation is determined by deduction from this size of the number 2. A high bound is known by addition of the number 5. As a result get a number 7, that number of days, when it is more frequent than all conception can come.
Method 2
From the number of days of cycle subtract 16, getting the first border. The second border is determined by addition to the got sum of the number 4. For greater safety add for 3 days yet.
A temperature method is based on determination of time of getting up of basal (rectal) temperature by its daily measuring, and abstention from carnal knowledge in the first phase of menstrual cycle, including the first three days getting up of basal temperature after ovulation. In 3 days after getting up of temperature (marking the last ovulation) an ovule loses a capacity for the impregnation, and the danger of offensive of pregnancy disappears. Sexual life without additional contraception is possible after this time. Although this method has some inconveniences related to the necessity of the daily measuring of basal temperature, efficiency of him is great enough.
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