The Ratio of Clavicle Length to Head Circumference: A Novel Date-Independent Clavicle Index.

We aimed to plot the growth curve of the fetal clavicle, identify gestational date-independent parameters. Using 2-dimensional ultrasonography, we obtained the clavicle lengths (CLs) from 601 normal fetuses between 12 and 40 gestational age (GA). The CL/fetal growth parameters ratio was calculated. Moreover, 27 cases of fetal growth restriction (FGR) and 9 cases of small for GA (SGA) were detected. In normal fetuses, the mean CL (mm) = -68.2 + 29.80 × ln(GA) ± Z × (1.07 + 0.02 × GA). A linear relationship was detected between CL and head circumference (HC), biparietal diameter, abdominal circumference and femoral length with R2 values of 0.973, 0.970, 0.962, and 0.972, respectively. The CL/HC ratio (mean value 0.130) showed no significant correlation with GA. Clavicle lengths in the FGR group significantly decreased compared with the SGA group (P < 0.01). This study determined a reference range of fetal CL in a Chinese population. Furthermore, the CL/HC ratio, which is independent of GA, is a novel parameter for the evaluation of the fetal clavicle.