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What Does Low CI In An Ultrasound During Pregnancy Indicate?

Posted on Tue, 20 May 2014

Question: I am concerned about an ultrasound result. As you can see on the attached table, over the first two of the last three ultrasounds, the CI was in the normal range [I calculated these figures using this formula: (BPD/OFD)*100]. However, on the last US, the BPD barely increased at all, while the other figures did; this resulted in a much lower CI. It would seem that each of the measurements, taken individually, is in the normal range. The concern is simply with that formulation of the CI and what that could signify.

Answered by Dr. Mahesh Koregol (31 minutes later)

Brief Answer:
CI

Detailed Answer:
Hi,

I read your query and I understand your concerns.

Following is my reply:

1) CI ( Cephalic Index) measures proper proportion of head size. Your formula is right.

2) It calculates transverse and longitudinal diameter of the head.

3) BPD ( Biparietal diameter) has increased to some extent and it is very early to accurately measure the BPD as few mm error is expected at this stage and hence the little increase.

4) CI needs to be in the range of 74 to 83 which is normal. As per your report its in normal range.

5) CI signifies shape of the head and if any gross abnormalities present in the shape. It is normal in your baby. Hence dont worry about it.
4)

Let me know if you have anymore questions.

Regards,
Dr. Mahesh Koregol

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Mahesh Koregol (3 minutes later)

Thanks. However, per your #4 above, the last result was *not* normal (it is 70.4), although the underlying measurements (BPD and OFD) are in the normal range. What does it mean when BPD and OFD are, by themselves, normal, but when joined in the formula, produce a lower than normal CI?
Also, by the way, the baby's head *appeared* normally shaped on the US. Just confused about the CI of 70.4

Answered by Dr. Mahesh Koregol (9 minutes later)

Brief Answer:
Range

Detailed Answer:
HI,

All measurements have a certain range of normality. Hence individually all parameters did appear normal and hence head shape appeared normal.

Though 70.4 is little below normal it is not alarming because the individual diameters are important and CI is not extremely standard and not made for small differences as in your case. More over in this gestational age few mm of error is possible while scanning and hence can be ignored.

If there was abnormal head shape you generally see gross variations in CI value. Hence as of now you dont need to worry for 70.4 value.

Regards

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar