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A 24-year-old female asked:

Can the ultrasound be off by 8 weeks in the 2nd trimester?i mean if all ultrasounds match with the dates the preg. can actually be further along?

3 doctor answers5 doctors weighed in
Dr. Warren Everett
Specializes in Family Medicine
Very unlikely: ultrasound should be reliable within 2 weeks at this point, 8 weeks is very improbable
Dr. Carrie Cannon
A Verified Doctoranswered
Family Medicine 33 years experience
One week max: I think 8 weeks off between dates and ultrasound is unlikely. The maximum I've read in studies so far has been 6 days off with accurate dates. Are you sure when your last menstrual period began?
Dr. Carrie Cannon
A Verified Doctor commented
A US doctor answered Learn more
Provided original answer
I hope you sleep soundly tonight. Take care.
Aug 26, 2014
Dr. Leila Hashemi
Internal Medicine 21 years experience
Due date & Ultrasoun: Earlier ultrasounds are more accurate for predicting the due date, still it could be off by 1 & half wk, between 18-28 wks the margin of error increases to 2 wks and after that up to 3 wks but not more than that. That's why doctors will usually use the dates and measurements from the first ultrasound of the pregnancy as a reference.

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