NT Measurement Between 3 and 3.4mm: A Risk for Abnormal Fetal Chromosome Findings?
BACKGROUND AND PURPOSE:
There are differing nuchal translucency (NT) measurement thresholds for offering invasive diagnostic testing
Sagi-Dain et al. (Obstetrics & Gynecology, 2021) examined the risk for clinically significant chromosomal microarray findings in fetuses with NT measuring 3.0 to 3.4 mm
Retrospective cohort study
Chromosomal microarray analysis tests performed due to NT measurement from 3.0–3.4 mm
No fetal structural anomalies seen on ultrasound
The authors compared rates of clinically significant microarray findings against a previously published local control population
Control population had normal ultrasound findings and NT <3.0 mm
Clinically significant microarray findings were defined as pathogenic and likely pathogenic copy number variants (CNVs)
Yield of NIPT was also assessed
619 chromosomal microarray analyses were included
Cases with nuchal translucency from 3.0 to 3.4 mm had significantly higher risk for significant CNVs
Study population: 4.7% (29 cases) with CNVs
Relative risk 3.3 (95% CI, 2.6 to 7.2)
Relationship between each millimeter increment and increased risk for significant CNV
NIPT and/or karyotype
NIPT including 5 common chromosome aneuploidies could in theory have detected 17 of the abnormal cases
41.4% of the abnormal CNVs would be missed | Represents 1.9% of NTs measuring 3 to 3.4 mm
Genome-wide NIPT or traditional karyotyping
Would have detected an additional 3 cases
Would have missed the remaining 9 cases that could only be detected with microarray
Isolated NT between 3.0 and 3.4mm is associated with increased risk for CNVs compared to a historic control cohort
For fetuses with normal ultrasound and NT between 3.0 and 3.4mm
NIPT could miss 1.94% of fetuses with abnormal findings
Genome-wide NIPT or karyotype could miss 1.5% of fetuses with abnormal findings
The authors state
Our results support 3.1 mm as the cutoff for abnormal nuchal translucency
In addition, because more than 40% of the fetuses with clinically significant chromosomal microarray analysis results would be missed by NIPT, it seems that cell-free DNA testing may not adequately replace invasive testing for chromosomal microarray analysis in such cases
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