Fetal Growth Discrepancy: Understanding Measurement Inaccuracies & Ultrasound

Question
Dear Dr. Rappaport, I am 32 weeks pregnant and had a doctor's appt. this morning.  They say I'm measuring at 34 weeks so they have scheduled an ultrasound to be sure.  Just wondering if I am simply measuring large due to position of baby or could I be carrying a large baby (my 2 children from previous marriage were 9 lbs 5oz and 8 lbs 14 oz respectively).  Thank you.

Jeanne  

Answer
At 32 weeks gestation, a sonogram is grossly inaccurate in determining how large the baby is or what your gestational age is. The most accurate time for a sonogram is at 20 weeks or at 16 weeks from the first day of your last period. Also, subjective measurement by a doctor or nurse is difficult to standardize, whether it is done with a tape measure or by measuring the number of fingers above your belly button or below your sternum. (Five different examiners may come up with five different sizes). Certainly, serial sonograms can be done to see if there is adequate growth from one week to several weeks later. You certainly may be carrying high or it may be a large baby. A biophysical profile with an estimated fetal weight may clear things up. I would also get an amniotic fluid index to see if you may have an overabundance of amniotic fluid.