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A member asked:

In my scan @21 weeks 4 days fetus has bpd50mm, hc183mm, fl33mm, ac156mm and fetal age is 20weeks 4days but this lags a weeks as per my lmp..is it ok?

2 doctors weighed in across 2 answers

Ultrasound dates: 2nd trimester ultrasound has an accuracy window of +/- 2 weeks so a one week discrepancy is acceptable!

Dr Accurso agreed

Answered 5/8/2014

5k views

Thank
Dr. Joseph Accurso answered

Specializes in Radiology

LMP dating vs US: Both methods have some error. Us dating is most accurate between 8 and 13 weeks using the crown rump length of the fetus. If us and LMP dating are different by more than 2 weeks, the accuracy of LMP dating should be questioned. Us is +/- 8% accurate, so at 21w4d, 95% confidence range would be 19w6d to 23w2d.

Answered 2/13/2015

5k views

Thank

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