Serial ultrasonic measurements were performed in 67 Caucasian fetuses
from 20 weeks' gestation until term to derive reference standards for
abdominal circumference (AC) and estimated fetal weight (EFW). The var
iances of both AC and EFW increased with gestational age. Four mathema
tical models (linear, quadratic, Gompertz and Rossavik) were fitted to
the log10(AC) and log10(EFW) data from each fetus using least squares
regression analysis. The standard deviations of the residual error we
re greatest for the linear model. The linear model also overestimated
the final log10(AC) while the linear, Gompertz and Rossavik models all
overestimated the final log10(EFW) when these data were omitted from
the fitting process. The individual quadratic constants were, therefor
e, used to produce 67 individual growth curves. Values Of log10(AC) an
d log10(EFW) for each fetus at exact gestational ages between 20 and 4
0 weeks were derived by interpolation; the mean and standard.deviation
values were then used to derive centile ranges for abdominal circumfe
rence and estimated fetal weight. These standards should prove useful
in the assessment of fetal growth.