- Use in cases of unusual head
- 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.
- Measure at the same level as
- Widest transverse and longitudinal
(frontal-occipital diameter, FOD) diameter of the cranium at the level of
- Measure from outer to outer
margins of the fetal cranium.
- CI = BPD/FOD X 100
- Normal = 78.3 ±1SD (74-83).
- < 74 =
- > 83 =
- 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.