The differential enlargement of the neurocranium in the full-term fetus.

There is a wide range of variation in the cephalic index in the full-term fetus. The index rises as birth weight increases. The correlation between birth weight and the cephalic index is significant (r = 0,65) at the 0,05 level. Increasing neurocranial size is associated with differential growth of the dimensions which determine endocranial capacity. A higher cephalic index is achieved by a disproportionately large increase in the biparietal diameter relative to the occipitofrontal dimension. This results in a more globular neurocranial form.