Ultrasonic measurement of the growth of fetal limb bones in normal pregnancy.

From sonographic measurements, normal curves for the fetal growth of extremity bones (humerus, ulna, radius, femur, tibia) were established. They are based on 40 measurements for each bone weekly between the 17th and 41st gestational week. Tabs. II and III summarize the data. Figs. 4-8 furnish the smoothened normal curves for 10th, 50th and 90th percentile. Values for the 14-16 and the 42nd week were extrapolated from the results and the course of the curves. A comparison of sonographic measurements with findings from dissected stillborn fetuses (Tab. I) demonstrated an accuracy of the sonographic measurements of +/- 2 mm. We established that the radius is significantly shorter than the ulna (Figs. 1 and 2) whereas tibia and fibula are of identical length (Fig. 3). The growth rate of the femur throughout pregnancy is greater than that of the other bones. The mathematical correlation between pregnancy duration and length of bones is best described by polynomial formulas (Tabs. IV and V), because the growth rate declines from 4 mm per week in early mid-trimester to 1 mm per week toward the end of the third trimester. A comparison with other published data shows the values in the current study to be within the range of variability of these publications. Sonographic measurements of extremity bones are suitable for determining gestational age.