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CEPHALIC INDEX (CI) |
- Use in cases of unusual head shape.
- Use to discriminate between a normal fetal head shape and a head that is abnormal enough to alter the estimation of the fetal age based on the BPD.
- CI is the relationship between the short and long axes of the fetal cranium.
LANDMARKS
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- Measure at the same level as the BPD.
MEASUREMENT
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- Widest transverse and longitudinal (frontal-occipital diameter, FOD) diameter of the cranium at the level of the BPD.
- Measure from outer to outer margins of the fetal cranium.
- CI = BPD/FOD X 100
- Normal = 78.3 ±1SD (74-83).
- < 74 = Dolicocephaly.
- > 83 = Brachycephaly.
- Cephalic index
(Table)– Gray et.al. 1987
- Cephalic index (Graph)– Gray et.al. 1987
- CI is within 1 SD of the mean with a sensitivity of 84% and a false positive rate of 35% for detection of a misleading BPD value.
