I notice on my ultrasound scan at the top, it say "ga(lmp)=06w6d" what does that mean? is that a measurement of the baby determined by the ultrasound?

Gestational age (GA): = how many weeks pregnant you are from the first day of your last menstrual period (lmp) to the date of the exam. It estimates your due date within 4-6 days. Full term gestation = 38-42 weeks. Conceptional age = time since implantation, often known when assistive reproductive techniques are used. It's 2 weeks < than gestational age. The baby center's free app, " my pregnancy today" is useful.

A measure of age: Ga stands for gestational age which is a measure of the age of the baby. Lmp stands for last menstrual period. This age measure is determined from the time of your last menstrual period. There is likely another age measure somewhere on the report that estimates age from a measurement on the ultrasound.

Dating based on LMP: That is the gestational age of the fetus based on the first day of your last menstrual period. However in the first trimester, they would use the measurements of the fetus (typically the crown to rump length in the first 12 weeks) to determine the gestational age and therefore the estimated date of delivery because it is more accurate.