When you get an obstetrical ultrasound, does the machine add one or two weeks gestation? Today it said I was 5weeks5days and I was on my period then

Gestational age. When we talk about gestational age, we count for the first day of your last menstrual period. That convention goes back to the days before we understood when ovulation and conception occurred, and the only event we had to go by was the LMP. Now we understand that ovulation occurs two weeks later. So, if you were 5 weeks and 5 days, then conception occurred about 3 weeks and 5 days ago.