Utility of fetal anteroposterior to transverse cerebellar diameter ratio to exclude cerebellar hypoplasia in trisomy 18.

This study shows that TCD and APCD are correlated with GA, while the APCD/TCD ratio is a fixed value throughout gestation. Using the APCD/TCD ratio to assess cerebellar hypoplasia in trisomy 18 is useful because it does not require the individual evaluation of the TCD and APCD.