Hi!
In many cases, when a discrepancy like this occurs, it is due to the position the baby was in at the time of the scan, or the quality of the scan. The first thing I usually do is to repeat the ultrasound after a few weeks. If a discrepancy persists, the next most common thing is that the baby is going to be petite--especially if the parents are not tall people themselves.
Finally, if the discrepancy is large (yours is not) I might refer the patients to a high risk doctor and genetic counselor for further evaluation.
Good luck!
Dr B
thank you so much i feel much better already,im going for my repeated scan this thursday and i dont feel as anxious about it now!thank you, much love