The significance of fetal sacral length in the ultrasonographic assessment of gestational age.

Objective: The present study aims to establish a more sensitive nomogram of fetal sacral length measurements, as well as to specify the accuracy of fetal sacral length for the ultrasonographic assessment of gestational age.

Methods: The present study investigated a total of 2,184 pregnant women who were referred for routine pregnancy follow-up. All of the reviewed women had uncomplicated singleton pregnancies without known structural and chromosomal fetal anomalies.

Results: A statistically significant linear relationship was established between sacrum length and gestational age [gestational age = 4.49 + 0.92 × sacrum length (r = 0.98, R (2) = 0.96)]. The rate of increase in sacrum length of fetuses with a gestational age of < 28 weeks was formulated as [gestational age = -0.05 + 1.01 × sacrum length (r = 0.96, R (2) = 0.98)], while the same formula was [gestational age = -0.09 + 1.32 × sacrum length (r = 0.94, R (2) = 0.96)] for fetuses with a gestational age of ≥ 28 weeks. On the other hand, a statistically significant correlation was found to exist between biparietal diameter (r = 0.68, P = 0.001), head circumference (r = 0.590, P = 0.001), femur length (r = 0.719, P = 0.001) and sacrum length (r = 0.696, P = 0.001). However, the same statistically significant correlation exists between abdominal circumference and the other sonographic measurements (r = 0.223, P = 0.375).

Conclusions: The fetal sacral length appears as an easily acquired and valuable parameter, which directly and strongly correlates with gestational age and other biometrical measurements. Therefore, fetal sacral length may be utilized as a complementary tool in both the evaluation of fetal growth and prediction of gestational age. Further research is required to determine the significance of fetal sacral length in prenatal follow-up.