Fetal sacral length in the ultrasonographic assessment of gestational age

Abstract

Our purpose was to establish a nomogram of fetal sacral length throughout gestation and to assess its value in cases of abnormal fetal growth. A prospective cross-sectional study of 506 singleton fetuses with normal growth between 15 and 41 weeks' gestation was performed. Regression analyses were performed on sacral length, gestational age, biparietal diameter, head circumference, and femur length. The sacral length in 80 singleton gestations with abnormal growth (40 > 90th percentile and 40 < 10th percentile for gestational age) were compared with the nomogram. Linear relationships between gestational age and sacral length, biparietal diameter, head circumference, and femur length were demonstrated. Sacral length (centimeters) as a function of gestational age (weeks) was expressed by the regression equation: Sacral length = -0.108 + 0.102 Gestational age, with a Pearson correlation coefficient of R2 = 0.959. The sacral length of all 80 fetuses with abnormal growth demonstrated the same relationship to gestational age as did the 506 normal controls. This study defines the normal limits of sacral length; demonstrates a high correlation between sacral length, gestational age, and other standard measurements of fetal growth; and indicates that sacral length can predict gestational age, irrespective of fetal nutritional status.