Head Circumference

HEAD CIRCUMFERENCE

Head Circumference (outer perimeter of the fetal cranium measured at the level of the BPD)

Very reliable indicator of gestational age as it is less dependent on the shape of the head than the BPD.
It is superior to the BPD in predicting the gestational age of the fetus.
Useful when cephalic index is
<70 (dolicocephaly/ scaphocephaly) or when it is
>86 (brachycephaly).

22 wks	30 wks

Head circumference should be traced along the outer perimeter of the calvarium using a map reader or electronic ellipse.
Alternatively it can be calculated from:
HC = 1.57 X outer-to-outer edge BPD + outer-to-outer OFD.
Normal Values of Head Circumference (Tables / Graphs)

Variability (± 2SD, wks)

12-18 wks ± 1.3 wks

18-24 wks ± 1.6 wks

24-30 wks ± 2.3 wks

30-36 wks ± 2.7 wks

36-42 wks ± 3.4 wks