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 were analyzed. Abnormalities included trisomy 21 ( n = 23), trisomy 18 ( n = 17), 'other numerical chromosomal abnormalities' ( n = 9), sex chromosomal abnormalities ( n = 9), mosaicism ( n = 12), balanced translocations ( n = 9) and unbalanced translocations ( n = 9). Multiple regression analysis was performed to compare transcerebellar diameters between the reference group and each of the subsets of chromosomal abnormalities and between trisomies 18 and 21. Also, in the latter two subsets, comparison of the transcerebellar diameter before and after 25 weeks of gestation was carried out.
Results: Fetal transcerebellar diameter was reduced in relation to gestational age but was normal when control was made for fetal size in all chromosomal subsets, except for balanced translocations. The transcerebellar diameter in trisomy 18 was significantly smaller than that in trisomy 21. No difference in cerebellar size was found when comparing the gestational age period 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. Cerebellar hypoplasia was more severe in trisomy 18 than in trisomy 21. The degree 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.