hello i am in 38 weeks and sonography report shows gestational age 35 week lac of 3 weeks and small for date what is it exactly mean?? why it happens?

A. Scans done at 40 weeks and beyond were more accurate than those done preterm. Only 81% of the scans done between 34 and 37 weeks gestation fell within the accepted 15% margin of error between EFW and actual weight compared to 100% when the scan was done after 40 weeks.