[Clinical study and prenatal diagnosis of fetus with shortened long bones]

To investigate the manifestations and prenatal diagnosis of the fetus with shortened long bones.

Ultrasonography was conducted on 57 fetuses with shortened long bones and 62 normal fetuses. Percutaneous umbilical blood sampling was performed on the 57 cases to undergo examination of karyotype and mutation in exon 10 of fibroblast growth factor receptor (FGFR)3 gene. Fetal radiography and autopsy were performed in 30 abnormal induced fetuses.

Among the 57 fetuses of the shortened long bones group 21 (37%) were diagnosed as with specific skeletal dysplasia postnatally, abnormal chromosome were found in 8 (14%), 4 (7%) were with fetal growth restriction, and 24 (42%) were with unknown etiology. Prenatal ultrasonography showed that in the fetuses with skeletal dysplasia the value of standard deviation score (SD) for femur length and/or humerus length fell to -4 SD of the corresponding pregnancy week, and increase of biparietal diameter was often found; in the fetuses with abnormal chromosome and fetal growth restriction (FGR) the degree of bone shortening was between -2 SD to -4 SD; and in the fetuses with lethal skeletal dysplasia the long bones were shortened at the degree more than -8 SD. When the ratio of femur length to abdominal circumference was less than 0.16, the sensitivity and specificity for predicting narrow thorax were 100% and 85.7% respectively.

The causes of fetus with shortened long bones include abnormal chromosome, skeletal dysplasia, and FGR. Femur length and/or humerus length falls below -4SD is almost an indication for skeletal abnormality. When the SD is between -2SD and -4SD, chromosome analysis is necessary and regular ultrasonography is recommended. When the femur length and/or humerus length is below -8SD and femur length/abdominal circumference (FL/AC) is less than 0.16, lethal skeletal dysplasia is suspected.