Transverse cerebellar diameter: a useful predictor of gestational age for fetuses with asymmetric growth retardation.

There have been conflicting reports regarding the ability of cerebellar diameter to satisfactorily predict the gestational age of growth-retarded fetuses. Gestational age prediction intervals were derived from 270 normal fetuses between 14 and 40 weeks' gestation for biparietal diameter, head circumference, abdominal circumference, femur length, and transverse cerebellar diameter. We evaluated the ability of these parameters to predict gestational age for 19 small-for-gestational-age fetuses. The cerebellar diameter regression model led to the smallest differences between observed and predicted gestational age for all growth-retarded fetuses. Transverse cerebellar diameter satisfactorily predicted gestational age for all six fetuses with asymmetric intrauterine growth retardation and was associated with the least amount of underestimation bias when compared with other ultrasonographic parameters. However, transverse cerebellar diameter appeared to be no better than biparietal diameter, head circumference, or femur length for accurately predicting gestational age of fetuses with symmetric intrauterine growth retardation (n = 13) despite the finding that cerebellar growth was also relatively spared under these circumstances. We conclude that transverse cerebellar diameter can be used to reliably approximate gestational age in fetuses with asymmetric intrauterine growth retardation. However, caution is warranted when using it to predict the gestational age of fetuses affected by symmetric intrauterine growth retardation.