Fetus measurement

I had an ultrasound, my results were the following:
Pregnancy: 22,2 weeks
BDP- 49
HC- 144
AC-173
FL-37
PTM- 460g

Is that normal? Is the head circumference too small or not comparing to the body? Oh, yes, my placenta is positioned very low, and the baby is very low also. I have no other problems, i try to eat healthy, i have no genetic problems in my family. I am worried that the babys head is too small, or am i just exagerating?
Thank you very much in advance for your prompt answer!

[Elaine Brown, MD]

Hi!
The BPD is at the lower limits of normal for that gestational age--there could be very many factors influencing the measurement though--the MOST likely being the technique of the sonographer.  I almost NEVER get concerned about measurements obtained on only one scan, the first thing I would do is wait 3-4 weeks and repeat the scan. It is very likely that the baby is just fine.  Also, the placenta moves up the uterine wall as the baby grows and the uterus expands, so in close to 99% of cases it is well out of the way by the time the baby is due.  As far as carrying the baby low, there are lots of wive's tales about the meaning of this, but medically there is no significance.
Be sure to ask your own doctor about all of this too!
Good luck!
Dr B