Oh what I meant by my rambling is, the answer to your question is BOTH...gestational age 6 1/2 weeks, fetal age 4 1/2 weeks.
Sorry for rambling :)
They go by gestational age, dating from the first day of your last menstrual period. Fetal age is from date of conception. The reason doctor's use gestational age is because MOST women don't know when they conceived but do know when they had their last period.
Since ovulation is usually around day 14, fetal age is approximately 2 weeks less than gestational age. I thought that was really weird...when I ovulated I entered that date as date of conception and the due date estimator said I was already two weeks pregnant...and I was kind of like "Umm...baby is two cells and dividing rapidly...HOURS not weeks...weird" but due date estimators give gestational age, not fetal age.
Congratulations! Adgal is right. They count from the first day of your last period.
Wish you a happy and healthy pregnancy! :)
They count from the first day of your last menstrual period. When you hear about heartbeats being seen at 8 weeks, it is 8 weeks from lmp. For the average women that is about 6 weeks from conception. But they always talk in terms of weeks since first day of last menstrual period. You are both right...babies gestational age would be 4 1/2 weeks, but you are still 6 1/2 weeks which is how your Dr. will refer to it. This is because it is virtually impossible to pinpoint the moment of conception.