3 doctors weighed in:
Pregnancy ultrasound dating accuracy?
3 doctors weighed in

Dr. Miguel Cano
Obstetrics & Gynecology
1 doctor agrees
In brief: Earlier the better
In the first trimester (< 14 wks) it's accurate within days.
The later in pregnancy, the more inaccurate it is to date a pregnancy. Roughly, if an ultrasound differs by a week in the first trimester, dates are changed. 2 weeks for second trimester & 3 wks difference in the third trimester to change the due date compared to an lmp due date. Always keep the earliest us edc, it should never change.

In brief: Earlier the better
In the first trimester (< 14 wks) it's accurate within days.
The later in pregnancy, the more inaccurate it is to date a pregnancy. Roughly, if an ultrasound differs by a week in the first trimester, dates are changed. 2 weeks for second trimester & 3 wks difference in the third trimester to change the due date compared to an lmp due date. Always keep the earliest us edc, it should never change.
Dr. Miguel Cano
Dr. Miguel Cano
Thank
Dr. Jumnah Thanapathy
Obstetrics & Gynecology
In brief: Depends
Upon when it is done. The earlier it is the more accurate the dating.

In brief: Depends
Upon when it is done. The earlier it is the more accurate the dating.
Dr. Jumnah Thanapathy
Dr. Jumnah Thanapathy
Thank
Get help from a real doctor now
Dr. Dennis Higginbotham
Board Certified, Obstetrics & Gynecology
26 years in practice
49M people helped
Continue
108,000 doctors available
Read more answers from doctors