Fetal weight-cerebellar diameter discordance as an indicator of asymmetrical fetal growth impairment.

In this study on the effect of fetal growth impairment < or = 25th percentile on the transverse cerebellar diameter and its relationship with other fetal biometric parameters, the sample comprised 50 women with singleton pregnancies referred for ultrasound evaluation because of clinically suspected intrauterine growth retardation. The cerebellar diameter of asymmetrically growth-impaired fetuses remained within the normal range although it was found to be reduced when compared with that of normal fetuses (4.4 +/- 0.9 versus 4.8 +/- 0.7, P < .05). Although other biometric parameters (biparietal diameter, femur length and abdominal and head circumferences) were also reduced in growth-impaired fetuses, the ratios of these biometric parameters to cerebellar diameter were similar to those of unaffected fetuses. Fetal weight was affected to a greater extent than the cerebellar diameter, leading to discordance between the two parameters. This discordance identified almost all asymmetrically growth-impaired fetuses with a sensitivity of 95.6% and specificity of 96.3%. In contrast, the ratio of head circumference to abdominal circumference remained normal in more than half of the fetuses. Fetal weight-to-cerebellar diameter discordance is a very sensitive and specific indicator of asymmetrical fetal growth impairment.