Ultrasound question

[ivygrimes]

When you have your first scan at the 6 or 7 week mark.
How is it the sonograph calculates the pregnancy as 7 weeks rather than the age of embryo?
I know, 40 week pregnancies etc, but that's based on the unknown ovulation conception date.

I get how a non-IVF ultrasound automatically adds 2 weeks on to the gestational age but why for non IVF when the lab techs have calculated things exactly as they should be?
Or do all sonograph readings simply calculate extra 2 weeks as an autorule type thing?

[Tashtash]

When you have your first scan at the 6 or 7 week mark.
How is it the sonograph calculates the pregnancy as 7 weeks rather than the age of embryo?
I know, 40 week pregnancies etc, but that's based on the unknown ovulation conception date.

I get how a non-IVF ultrasound automatically adds 2 weeks on to the gestational age but why for non IVF when the lab techs have calculated things exactly as they should be?
Or do all sonograph readings simply calculate extra 2 weeks as an autorule type thing?

I can’t find specific links now to the websites I looked at as I wondered this a while ago but in short from what I recall because you go back to the nhs as well after, all women are treated the same no different because it was ivf vs natural so it is taken from the date of your last period because normally they don’t know exactly when the embyro has implanted and I think for the sake of not making things complicated its a one size fits all so it actually makes you further along then you think you are but take into account your eggs being fertilised in the lab etc its like it being fertilisied in the body and travelling down the fallopian tube to implant its just r know the exact date it likely implanted. Does that make sense