Are abdominal ultrasounds as accurate for dating as vaginal around 11 weeks of pregnancy? what is the margin of error for abdominal at this gestation?

Depends: If a woman is thin and the doctor has a good image of the fetus, then abdominal can be just as accurate as vaginal. Margin of error at this gestation is still +/- 5 days. After 14 weeks that number increases to +/- 10 days.

Yes, if...: An abdominal ultrasound at 11 weeks is just as accurate for dating as vaginal (+\- 1 wk) if the image quality is good. You can see early fetal anatomy much better vaginally though.