A longitudinal study of fetal head biometry.

In this paper the results gathered in a longitudinal ultrasound study (LS) of fetal growth are presented. The study is unusual in design because of its homogeneity, the number of parameters recorded, the exact spacing between the examinations, and the number of examinations per subject. Information not available in the usual cross-sectional studies (CSS) are reported. They include: improved fit of equations with better description of extreme values; absence of increase of the standard deviation, which is in sharp contrast with the CSS published to date; and analyses of growth velocity that are not available in CSS. The parameters that will be reported in this section include the biparietal (BPD), the occipitofrontal (OF), the head perimeter (HP), and the cephalic index (Cl).