In a prospective study of 330 pregnant women, measurements of the transverse cerebellar diameter (TCD), abdominal circumference (AC), biparietal diameter (BPD), head circumference (HC) and TCD/AC ratio and HC/AC ratio were obtained using conventional ultrasonography between 16th and 41st weeks of gestation. Measurement of BPD yielded a strong correlation with gestational age (r = 0.9880 and R2 = 0.9761) by cubic regression analysis. The measurement of TCD also had a very close relation with gestational age (r = 0.9767 and R2 = 0.9539). The ratio between TCD and AC was calculated and found to be 0.1436 ± 0.0106 (SD) which remained fairly constant throughout pregnancy, while the BPD/AC ratio declined. The 5th and 95th percentiles for this ratio were 0.1279 and 0.1603. Ten of eleven fetuses with TCD/AC ratios exceeding 2 SD (0.1648) were found to have asymmetrical intrauterine growth retardation upon neonatal examination. It is demonstrated that both BPD and TCD measurements are reliable techniques that correlate well with gestational age, and the TCD/AC ratio is valuable in identifying babies with asymmetrical intrauterine growth retardation