When your dates are calculated from the LMP, this presumes that fertilisation occurs 2 weeks later.In many women, an ultrasound scan may shift their expected date of delivery (EDD), which comes as a surprise.This uses actual developmental stages to divide up a pregnancy.
There are basically three ways of dividing up a pregnancy into the three trimesters; they are by: Development, Gestation, Conception.
They give different dates for when the second trimester begins and for when the third trimester begins.
Your health care provider might prefer to use the Development method, while another Midwife or Doctor may use the Gestation method.
I am sure they do that just to confuse pregnant women.
If you have regular 28-day menstrual cycles, there are two ways to calculate your due date.
Naegele’s rule involves a simple calculation: Add seven days to the first day of your LMP, then subtract three months. This SD is to be converted into days’ gestation Hadlock F. Variation increases with increase in gestational age In late pregnancydifferent fetuses of same age are of different sizes Rule of 8 Hadlock regression analysis USG gestational age estimation is consistently accurate with 8% margin of error irrespective of the GA. Other methods Prem’s rule –based on BBT7days subtracted from 1st day of thermal shift and 9 months added M G Hiremath (KIMS Hubli)pt is ignorant about English calendardoctor is ignorant about Lunar calendar! Error prone EDD not acceptable in modern times Katz VL et al Why we should eliminate the due date: A truth in jest. Methods of determining the gestational age Parameter Variability 2SD1st trimester USG –CRL ± 8% of the estimate 2nd trimester USG –HC, FL ± 8% of the estimate 3rd trimester USG – HC, FL ± 8% of the estimate Callen PW. Ovulation will have taken place roughly 2 weeks after this, so in effect pregnancy is about 38 weeks long.