Humerus, Femur Measuring small in sonogram

Hello!
I just had a 4 D sonogram on my own just to get pictures of the baby, I am 31 years old and 29 weeks and 4 days Due date 3/24/12. With the report below the sonogram pushed my due date to 4/6/12      
2 weeks more.  I received the report from them and I am concerned because my baby is measuring smaller than it should at this week. Now do you think this is just genetics or something of concern?  I am 5’8 and my hubby is about 5’5. I am 6-1/2 months prego and really not that big yet in the belly. I have been on Phenergan suppository 25 mg (Promethazine) for nausea since week 10. See my results below and let me know if you think that maybe my baby is just smaller/shorter or something to be concern??? (i am having a boy fyi.)
The rest of the report found everything to be normal, and I have not had any scares or issues during my pregnancy.
My results:
Femur Length 5.14 cm (27 w 3d)
Humerus Length 4.44 cm (26 w 3d)
Biparietal Diameter 7.13 cm (28w 4d)
Head Circumference 25.59 cm (27 w 6d)
Abdominal Cir 23.26 cm (27 w 4d)

[LovemyKids86]

Maybe your conception date is a little off. When I was 40 weeks measurements pushed my due date to a week later.