Prenatal Genetic Diagnosis of Fetal Cystic Hygroma: A Retrospective Single-Center Study from China.

Fetal cystic hygroma (CH) is associated with poor prognosis and chromosomal anomalies. Recent studies have suggested that the genetic background of affected fetuses is essential for predicting pregnancy outcomes. However, the detection performance of different genetic approaches for the etiological diagnosis of fetal CH remains unclear. In this study, we aimed to compare the diagnostic efficiency of karyotyping and chromosomal microarray analysis (CMA) in a local fetal CH cohort, and tried to propose an optimized testing strategy that may help improve the cost-effectiveness of disease management. We reviewed all pregnancies that underwent invasive prenatal diagnosis between January 2017 and September 2021 at one of the largest prenatal diagnostic centers in Southeast China. We collected cases identified by the presence of fetal CH. Prenatal phenotypes and laboratory records of these patients were audited, collated, and analyzed. The detection rates of karyotyping and CMA were compared, and the concordance rate of these two methods was calculated. A total of 157 fetal CH cases were screened from 6,059 patients who underwent prenatal diagnosis. Diagnostic genetic variants were identified in 44.6% (70/157) of the cases. Karyotyping, CMA, and whole-exome sequencing (WES) identified pathogenic genetic variants in 63, 68, and 1 case, respectively. The Cohen's κ coefficient between karyotyping and CMA was 0.96, with a concordance of 98.0%. Of the 18 cases in which cryptic copy number variants <5 Mb were detected by CMA, 17 were interpreted as variants of uncertain significance, and the remaining cases were interpreted as pathogenic. Trio exome sequencing revealed a pathogenic homozygous splice site mutation in the PIGN gene in a case undiagnosed by CMA and karyotyping. Our study demonstrated that chromosomal aneuploidy abnormalities are the main genetic cause of fetal CH. Based on this, we recommend karyotyping combined with rapid aneuploidy detection as a first-tier approach for the genetic diagnosis of fetal CH. WES and CMA could improve the diagnostic yield when routine genetic tests fail to determine the cause of fetal CH.