Fetal transcerebellar diameter and chromosomal abnormalities

Objective To evaluate the association between chromosomal abnormalities and fetal cerebellar size. Design A retrospective cross-sectional study. Methods Ultrasound measurements of transcerebellar diameter, head and upper -abdominal circumference from 88 fetuses with chromosomal abnormalities wer e analyzed. Abnormalities included trisomy 21 (n = 23), trisomy 18 (n = 17) , 'other numerical chromosomal abnormalities ' (n = 9), sex chromosomal abn ormalities (n=9), mosaicism (n=12), balanced translocations (n = 9) and unb alanced translocations (n = 9). Multiple regression analysis was performed to compare transcerebellar diameters between the reference group and each o f the subsets of chromosomal abnormalities and between trisomies 18 and 21. Also, in the latter two subsets, comparison of the transcerebellar diamete r before and after 25 weeks of gestation was carried out. Results Fetal transcerebellar diameter was reduced in relation to gestation al age but was normal when control was made for fetal size in all chromosom al subsets, except for balanced translocations. The transcerebellar diamete r in trisomy 18 was significantly smaller than that in trisomy 21. No diffe rence in cerebellar size was found when comparing the gestational age perio d before and after 25 weeks in each of these two subsets. Conclusions A reduction in fetal transcerebellar diameter was demonstrated in all chromosomal abnormalities with imbalance of genetic material. Cerebe llar hypoplasia was more revere in trisomy 18 than in trisomy 21. The degre e of reduction in fetal transcerebellar diameter in these subsets seems to be independent of the time period during which the transcerebellar diameter measurement was performed.