Fetal Growth Discrepancies: Understanding Ultrasound Inaccuracies

Question
This question is in regards to my daughter.  She is 30 weeks pregnant.  The baby's head is at 31 weeks.  The baby's stomach is at 27 weeks.  What problems could this be an indication of?
Thank you.

Answer
There is no problem. Sonograms are very inaccurate after 20 weeks gestation. The margin of error in a sonogram that is done as 30 weeks is + or - four weeks. We usually take an average of the biparietal diameter (the head), the abdominal circumference, and the femur length. Don't worry about it. The measurements arae all around 30 weeks. Use the gestational age based on the date of the first day of her last period.