WOMENS-HEALTH Messages for August, 2001: Re: 18 week ultrasound results

Re: 18 week ultrasound results

From: William McIntosh, MD (anonymous@obgyn.net)
Tue, 21 Aug 2001 12:50:08 -0500 (CDT)

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In reply to: Rebecca: "18 week ultrasound results"

At Tue, 21 Aug 2001, Rebecca wrote: >
>I just had my 18 week ultrasound and am quite confused by the results. T e doctor said everything is fine, yet I see that some of the measurement are outside of the norm.
>
>For example, BPD is 45.2 mm. What exactly is BPD?
>
>HC is 15.7 mm which is -.83 standard deviations from the norm.
>
>What does this mean? Is the baby's head quite small. I'm not certain as he BPD is above average and the HC is below average. Could you explain w at this means.
>
>Incidentally, femur length is 26.6 mm.
>
>Any feedback would be appreciated.
>Thanks
>Rebecca

I think that you are confused about what average means. The average denotes a single point, typically around the midpoint of a range. The values that you are telling us about are not exactly at the average point, but they are all well within the normal range for this gestational age, and there is no indication of abnormal or unusual growth. BPD stands for biparietal diameter, and is the measurement essentially from temple to temple. A standard deviation is a statistical term that shows how close a measurement is to the mean (average). Depending on what is being compared, "normal" is defined as being within at least 2 and usually 3 standard deviations of the mean. This is also a +/- sort of thing, going 2 or 3 standard deviations above AND below the mean. In your case, the head circumference is less than 1 standard deviation (-.83) from the mean, so your baby's head circumference is quite close to the average for his/her age.

The long and short of it is that the measurements appear to be entirely consistent with the baby's gestational age.

-- William D. McIntosh, MD, FACOG

This is for educational purposes only, and is not a substitute for consultation and examination by a licensed medical professional.

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