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Inherited Disorders and Birth Defects

Small BPD and head circumference

12/08/2006

Question:

I had my 22 week ultrasound and my baby`s head measured just below the 5th percentile...actually I believe it was the BPD (width) that was low. All other measurements seemed to be normal, but around the 10-20th percentile. I was not recommended an anmio, so what could the possible reasons for a descrepency be in the percentiles...? My midwife and dr. are content that all else looks good and that Doppler showed fine placental function. I can only imagine HC and brain growth are so closely realated and I am worried sick and considering a 2nd opinion...Can fetus` have growth spurts? Thanks for any imput

Answer:

Measurements taken on ultrasound during pregnancy usually include length (called crown-rump length), femur length (the thigh bone), abdominal circumference and biparietal diameter (the measurement from temple to temple - like a headband). It is the BPD that tells gives you a way of indirectly measuring the baby's head circumference. You mention that the BPD is just below the 5th percentile which still falls within the normal range. Also, having the other measurements plot out at the 10-20th percentile are not that much different from the BPD which perhaps is why your doctor did not seem concerned. If the other measurements were at the 75th or 90th percentile - that would be more concerning as that would be a true discrepancy between measurements or if the measurements were changing over time - if the BPD had been at the 75th percentile and now is at the 5th percentile.

It is difficult to say why the BPD measurement is somewhat lower than the other measurements and you are correct in that the BPD does give us clues as to how the brain is growing. While ultrasound is an excellent tool to provide us with information about the well being of a pregnancy, it is still like looking through a "veil" and not as good as looking at the baby after birth. Also, ultrasound is only as good as the people who are doing the ultrasound and the equipment that is used.

Getting a second opinion is always an option and may be very helpful in answering your questions more specifically than I am able to do.

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Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University