How to calculate term of sorts?

How to calculate term of sorts?
Pregnancy lasts on the average 40 weeks if readout to conduct from first day of last менструации. Prospective term of sorts is calculated by the doctor-accoucheur, to use more often so-called rule Негеля. To this rule 100 years. Calculation is conducted so: from the first day of last менструации count back at first three months, then to this term add 7 days. So, for example, if посленяя менструация has begun on April, 1st prospective day of sorts will be on January, 8th. Last statistical data about average duration pregnant completely prove such calculations.
If duration of a monthly cycle of future mother значителы differs from average duration in 28 days at calculation the prefloor гаемого day of sorts should be considered this factor. If duration kneading ного a cycle makes, for example, 3 weeks from calculated by rule Hei ля day of sorts take away week. Accordingly at a five-week cycle to the calculated term add 1 week. To name most exact it is possible де sorts if the woman that month when there was a conception, it is regular измеря morning temperature, i.e. a body temperature right after awakenings. To it is possible by day when the temperature has raised, easier to add 266 days. It is conducted by the most exact and probable date of sorts. It is necessary to know, however, that more often children are born all the same not this day calculated duly. True day of birth will be somewhere in an interval between the calculated day ро, plus-minus of 14 days.