After obtaining positive pregnancy test the age of the foetus is usually computed by identifying the first day of the last duration day, so the calculation begin with the initial day of the last period date in the variety of week, normally the maternity last for 40 weeks. So from the last duration we determine the age of the functions however this gets exact just when the individual is having a routine duration, when the durations are irregular be there is much less value to the last period date, the very first day of the last period usually is not very substantial since the egg is released 2 weeks prior to you miss your period. So we add two weeks to that, so if an individual is having regular duration that is every 28 days cycle then typically egg is released in 14 day, so 14 day behind and also 14 day ahead. So that counts to 4 weeks. The duration of females is around 45 days the egg is launched normally 31st day, so we do not have to compute the initial 31 days before that, so it will be the 31st day from there are 2 weeks a lot more. Than the calculation differs. For an usually regular cycle women the calculation is begun from the very first day of the last period and after that all these days can be affirmed as well as we do a very early maternity scan, normally the early maternity scan is a dating scan. We can get a precise reading by going via the very first day of the last duration date and also the very early pregnancy check.