When the ultrasound tech give you how many weeks you are is that going by gestation or conception?

Gestational age: Here in United States the gestational age is usually used calculated from the last menstrual cycle assuming that ovulation occurred on day 14. In european countries and in canada and many other countries conception age is used.

Gestation: The estimated age of the pregnancy given at the time of an ultrasound is from the time of the first day of your menstrual period. That makes it consistent with how obstetricians estimate your due date. Conception, on average, occurs 2 weeks after the first day of your menstrual period. That can vary from one woman to the next and is based on women who have a 28 day menstrual cycle. Hope that helps.