Head Circumference Is In The Low Percentiles

QUESTION

Dear Ms Ultrasound,
I am now 24 weeks pregnant. Last week my ultrasound showed head circumference in the 5th percentile. At 16.5 weeks it was at the 19th percentile, and at 20 weeks it was at the 13th percentile. Is it possible that when we go at 28 weeks for an ultrasound that this percentile will rise dramatically (30th percentile)? If it remains at the 5th percentile is there any reason to be alarmed? Any risks for cognitive delays? Why did these percentiles go down?

There are no other factors involved; the doctor doesn't see any other signs for him to be alarmed right now. I just need to be checked again at 28 weeks. Please help. Can you give me some information? This will be the longest month of my life to wait this long!

ANSWER

Hello, In our facility, we don't pay too much attention to the percentiles. If a woman is coming in for serial ultrasounds to monitor growth, we will take note of the percentiles but that's the only time.

The head circumference is the measurement that has some variations. This could be caused by the technician who measured that day, and where she chose to place the calipers along with many other factors. It doesn't necessarily mean something bad. Without specific measurements, head, body, femur, I don't really know exactly what the doctor is describing.If you are growing appropriately, the level of the amniotic fluid was fine, and there are no other problems I give you permission to STOP worrying as of now! Don't waste a month, a mental wreck, because of a "what if". I believe the baby does so much better developmentally, when Mommy is happy and stress free.

Regards,
-- Jane, RDMS

Jane Foley

Jane Foley has worked as a Sonographer (Ultrasound Technologist) since 1979. Jane has lived and worked in many parts of the world including Saudi Arabia. She is a Registered Diagnostic Medical Sonographer or RDMS. She pulls a wealth of information from her experience in the field of Radiology and her interactions with such a broad cross-section of cultures she has visited. She now makes her home on the island of Maui with her English husband, Michael.