U.S. doctors online nowAsk doctors free
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.

90,000 U.S. doctors in 147 specialties are here to answer your questions or offer you advice, prescriptions, and more. Get help now:

Ask doctors free
Educational text
Talk to a doctor
24/7 visits - just $39!
50% off with $15/month membership
Last updated Aug 14, 2018
Connect with a U.S. board-certified doctor by text or video anytime, anywhere.
24/7 visits - just $39!
50% off with $15/month membership


Content on HealthTap (including answers) should not be used for medical advice, diagnosis, or treatment, and interactions on HealthTap do not create a doctor-patient relationship. Never disregard or delay professional medical advice in person because of anything on HealthTap. Call your doctor or 911 if you think you may have a medical emergency.