Does isolated nuchal translucency from 2.5 to 2.9 mm increase the risk of fetal chromosome disease?

Associations between genomic aberrations, increased nuchal translucency, and pregnancy outcomes: a comprehensive analysis of 2,272 singleton pregnancies in women under 35

Objectives

Regarding increased nuchal translucency (NT), the cutoff values used are heterogeneous in clinical practice, this study aims to assess the efficacy of prenatal detection for chromosomal abnormalities and pregnancy outcomes in fetuses with varying NT thicknesses, in order to provide data that supports informed prenatal diagnosis and genetic counseling for such cases.

Methods

We included 2,272 pregnant women under 35 with singleton pregnancies who underwent invasive prenatal diagnosis between 2014 and 2022. The cohort comprised 2,010 fetuses with increased NT (≥2.5 mm) and 262 fetuses with normal NT but exhibiting a single soft marker. Prenatal diagnoses were supported by chromosomal microarray (CMA) and copy number variation sequencing (CNV-seq) analyses.

Results

The detection rates of numerical chromosomal abnormalities were 15.4% (309/2,010) and 17.3% (297/1,717) in the NT ≥2.5 and ≥ 3.0 groups, respectively. Pathogenic/likely pathogenic CNV incidence increased with NT thickness (χ2 = 8.60, p < 0.05), peaking at 8.7% (22/254) in the NT 4.5-5.4 mm group. Structural defects were found in 18.4% of fetuses with NT values between 2.5 mm and 2.9 mm. Chromosomal abnormality rates in the isolated increased NT groups of 2.5-2.9 mm and 3.0-3.4 mm were 6.7% (16/239) and 10.0% (47/470), respectively, with no statistical significance (χ2 = 2.14, p > 0.05). Fetuses with NT thickness between 2.5 and 2.9 mm combined with the presence of soft markers or non-lethal structural abnormalities exhibited a significantly higher chromosomal abnormality risk (19.0%) compared to fetuses with isolated increased NT ranging from 3.5 to 4.4 mm (13.0%). Pregnancy termination rates increased with NT thickness (χ2 = 435.18, p < 0.0001), ranging from 12.0% (30/249) in the NT 2.5-2.9 mm group to 87.0% (141/162) in the NT ≥ 6.5 mm group.

Conclusion

CMA or CNV-seq exhibited good performance in identifying genomic aberrations in pregnancies with increased NT thickness. NT ranging from 2.5 mm to 2.9 mm elevated the risk of fetal chromosomal abnormalities, particularly when combined with other soft markers.

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.