Further genetic testing in fetuses with increased nuchal translucency and a normal array: A targeted panel or exome?

When NIPT meets WES, prenatal diagnosticians face the dilemma: genetic etiological analysis of 2,328 cases of NT thickening and follow-up of pregnancy outcomes

Objective: To assess the performance of diverse prenatal diagnostic approaches for nuchal translucency (NT) thickening and to investigate the optimal prenatal screening or diagnostic action with a NT thickening of 95th percentile-3.50 mm. Methods: A retrospective analysis of 2,328 pregnancies with NT ≥ 95th percentile through ultrasound-guided transabdominal chorionic villus sampling (CVS), amniocentesis, or cordocentesis obtained clinical samples (chorionic villi, amniotic fluid, and cord blood), and real-time quantitative fluorescent PCR (QF-PCR), chromosome karyotyping (CS), chromosome microarray analysis (CMA), or whole exome sequencing (WES) were provided to identify genetic etiologies. Results: In this study, the incidence of chromosomal defects increased with NT thickness. When NT ≥ 6.5 mm, 71.43% were attributed to genetic abnormalities. The 994 gravidas with fetal NT thickening underwent short tandem repeat (STR), CS, and CMA. In 804 fetuses with normal karyotypes, CMA detected 16 (1.99%) extra pathogenic or likely pathogenic copy number variations (CNVs). The incremental yield of CMA was only 1.16% (3/229) and 3.37% (10/297) in the group with NT 95th percentile-2.99 mm and NT 3.0-3.49 mm, separately. Among the 525 gravidas with fetal NT thickening who underwent STR, CMA, and WES, the incremental yield of WES was 4.09% (21/513). In the group of NT 95th percentile-2.99 mm, there were no additional single-nucleotide variations (SNVs) detected in WES, while in 143 cases with NT of 3.0-3.49 mm, the incremental yield of WES was 5.59% (8/143). Conclusion: In the group of NT 95th percentile-3.0 mm, since chromosomal aneuploidy and chromosomal copy number variation were the primary causes and the additional contribution of CMA and WES was not significant, we recommend NIPT-Plus for pregnant women with a NT thickening of 95th percentile-3.0 mm first. In addition, comprehensive prenatal genetic testing involving CMA and WES can benefit pregnancies with NT thickening of 3.0-3.49 mm.

Increased use of diagnostic testing after increased nuchal translucency: The influence of non-invasive prenatal testing and chromosomal microarray

OBJECTIVE

The utilization of non-invasive prenatal testing (NIPT) and chromosomal microarray (CMA) has significantly altered the options for testing following the diagnosis of an increased nuchal translucency (NT). This study defines the rates of utilization of diagnostic testing in the pre-NIPT, pre-CMA, and post-CMA eras.

METHODS

We retrospectively examined NT scans performed in our department from January 2010 to December 2020 and identified all NTs ≥3.0 mm for analysis. We divided our data into three distinct periods (2010-2012, 2013-2016, and 2017-2020) corresponding to our institutional practice shifts in recommending and offering use of NIPT (2013) and CMA (2016), respectively.

RESULTS

689 patients with NT ≥ 3.0 mm met inclusion criteria in our study, of which 355 (51.5%) individuals underwent diagnostic testing and 334 (48.5%) did not. There was a significant decline in rates of diagnostic testing with NIPT (2013), which has returned to pre-NIPT levels with the availability of microarray.

CONCLUSIONS

Since the routine use of CMA (2016), the rates of diagnostic testing for increased NT have returned to pre-NIPT levels. This study validates data suggesting an initial decline in the rates of diagnostic testing following abnormal NT but suggests that the decline may be reversing in the post-CMA era due to a rise in rates of chorionic villus sampling.

Prenatal Diagnosis of Euploid Increased Nuchal Translucency on Fetal Ultrasound (I): Noonan Syndrome: Prenatal Diagnosis and Genetic Testing

Prenatal diagnosis of euploid increased nuchal translucency (NT) remains a challenge to obstetricians and genetic counselors although increased euploid NT at prenatal diagnosis can be associated with a favorable outcome. Prenatal diagnosis of euploid increased NT should include a differential diagnosis of pathogenetic copy number variants and RASopathy disorders (RDs) including Noonan syndrome (NS). Therefore, chromosomal microarray analysis, whole-exome sequencing, RD testing, and protein-tyrosine phosphatase, nonreceptor type 11 (PTPN11) gene testing may be necessary under such a circumstance. In this report, a comprehensive review of NS with its prenatal diagnosis and genetic testing is presented.