I had a 6 week ultrasound and 11 week for dating purposes, they were both high quality and put my conception on or about december 6, how accurate?

First trimester: Ultrasound measuring fetal crown-rump length is considered accurate to +/- 3 days or so. Personally i believe it is more accurate than that. Transvaginal ultrasound is generally much more trustworthy than abdominal. If the sonographer doesn't measure perfectly and correctly though, it can be off by more than a week. Hope this helps.

Excellent: The most accurate ultrasounds for dating a pregnancy are those done in the 1st trimester, which both of these scans were. A 6 week ultrasound can sometimes be a little early, depending on the size of the crown-rump-lenth, so getting another one at 11 weeks is great! the fact that these 2 ultrasounds agree means that you have very accurate dating. Good luck with pregnancy!

Very accurate: Early sonograms are very accurate for dating.