Cerebellar hypoplasia: could it be a sonographic finding of abnormal fetal karyotype in early pregnancy?

Objective: To evaluate the screening utility of early transvaginal measurement of transverse cerebellar diameter for the identification of fetuses with abnormal karyotype.

Methods: We retrospectively analyzed the transverse cerebellar diameters of 56 fetuses with abnormal karyotypes (study group) and 1,892 euploid fetuses (control group) at 11-16 weeks of gestation. A nomogram with confidence intervals (10th and 90th percentile) was established for transverse cerebellar diameters versus gestational age in the control fetuses and individual values for chromosomally abnormal fetuses were plotted. A regression equation of expected transverse cerebellar diameter for each gestational age was calculated from 100 euploid fetuses chosen randomly and applied to the remaining control fetuses and to the study group fetuses. The ratio of observed to expected cerebellar diameters was calculated in the control group and compared with those obtained in single chromosome anomalies.

Results: The measurements obtained in aneuploid fetuses are within the normal range for gestational age. Only in 2 of the 37 Down syndrome fetuses and in 2 of the 4 fetuses with trisomy 13 was the observed to expected measurement ratio below the 5th percentile for gestational age.

Conclusion: In our experience, the measurement of transverse cerebellar diameter cannot be considered as a useful tool in the detection of aneuploidy in early pregnancy. The data concerning trisomy 13 are too small, so that caution should be exercised when supposing an association between cerebellar hypoplasia detectable by early transvaginal scan and risk of this aneuploidy.