Transverse cerebellar diameter in small-for-gestational-age fetuses: pregnancy dating is possible only when growth retardation is secondary to uteroplacental insufficiency.

Abstract

The objective of this study was to establish whether measurement of the transverse cerebellar diameter to determine gestational age differs in small-for-gestational-age fetuses with normal or abnormal Doppler velocity waveforms. Our secondary objective was to compare the efficacy of measurement of transverse cerebellar diameter with that of femur length in pregnancy dating among small-for-gestational-age fetuses. A total of 107 small-for-gestational-age fetuses with established dates and free from structural and chromosomal abnormalities were considered for this study. According to the Doppler results, fetuses were divided into two groups: group A (n = 64), with normal Doppler values as expressed by a ratio of pulsatility indices between the umbilical artery and middle cerebral artery of <or= 95th centile of our reference limits for gestation; and group B (n = 43), with ratio of > 95th centile. Measurements of transverse cerebellar diameter and femur length were compared to previously established 95th centile prediction intervals. In both groups of small-for-gestational-age fetuses, the values for transverse cerebellar diameter were lower than in normally grown fetuses after normalization for gestational age. The difference was more evident in group A (p <or= 0.001) than in group B (p <or= 0.05). Only 68.7% of transverse cerebellar diameter values of group A fetuses fell within the normal limits for gestation, while this occurred in 90.6% of group B fetuses. When compared to the femur length, the transverse cerebellar diameter measurement appeared to be better for predicting gestational age in both groups of small-for-gestational-age fetuses (p <or= 0.001). However, this measurement may be used to estimate gestational age only in small-for-gestational-age fetuses with abnormal Doppler findings.