Prenatal diagnosis of achondroplasia and hypochondroplasia using three-dimensional computed tomography: a case series at a single institution

Fetal skeletal dysplasia (FSD) is a group of systemic bone and cartilage disorders that develop prenatally and can be detected using fetal ultrasonography. However, it is unsuitable for skeletal analysis because it is reflected by supersonic waves in the bone cortex. Three-dimensional computed tomography (3D-CT) is a suitable alternative and has improved the differential diagnosis of FSD during pregnancy. Achondroplasia (ACH) and hypochondroplasia (HCH) are the most frequent diseases in the FSD group. This study aimed to determine the efficacy of 3D-CT in the prenatal diagnosis of ACH/HCH.

Patients were selected for the study non-consecutively. Pregnant women who met the following selection criteria were included: (I) pregnancy at age ≥20 years at the time of consent; (II) fetal ultrasonography showing a short femur (below the 10^th percentile of fetal measurements) or an image of a long bone curvature or deformity; and (III) written informed consent to undergo 3D-CT. On suspicion of FSD based on ultrasonography, a 3D-CT scan was performed prenatally and an X-ray postnatally to obtain detailed skeletal information and to verify the shapes of all bones, respectively. A genetic examination was performed to confirm the diagnosis after obtaining informed consent from the parents. There were seven cases of prenatally diagnosed ACH/HCH. Genetic testing was performed in six infants postnatally, and a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene was detected [c. 1138G>A (p. gly380Arg)]. In one case, the patient was diagnosed with ACH and Down syndrome by genetic and chromosomal testing (G-band: 47, XY, +21).

3D-CT is a valuable and efficient tool for diagnosing ACH/HCH. Accurate prenatal diagnosis by gene analysis is crucial for a definitive diagnosis in infants.