Grand Rounds

Can NT Values be Used as an Indication for Prenatal Microarray Analysis?

BACKGROUND AND PURPOSE:

A correlation exists between nuchal translucency (NT) measurement and abnormal findings on chromosomal microarray analysis
3.5 mm NT measurement is currently used in many guidelines as the cut-off for further follow up studies even if found in isolation
Maya et al. (Ultrasound in Obstetrics & Gynecology, 2017) assessed different NT cut-off levels and their association with abnormal chromosomal findings on microarray

Retrospective, multicenter study
Pregnancies were divided in two cohorts:
- Normal NT and no other findings (underwent microarray testing at their own request)
- Increased NT as only indication for microarray analysis
- To reduce bias, cases with positive aneuploidy risk based on combined first trimester screening (NT + maternal serum markers) were excluded
NT measurements were divided into three groups:
- ≤ 2.9 mm
- 3.0–3.4 mm
- ≥ 3.5 mm
Primary outcome was chromosomal anomalies (pathogenic copy number variants [CNVs]) detected using microarray

770 pregnancies with increased NT and no other findings were analyzed
- 462 had NT ≤ 2.9 mm: abnormal microarray in 1.7%; 50% only detectable with microarray
- 170 had NT of 3.0-3.4 mm: abnormal microarray in 6.5%; 27% only detectable with microarray
- and 138 had NT ≥ 3.5 mm: abnormal microarray in 13.8%; 16% only detectable with microarray

CMA should be recommended when fetuses have an isolated NT thickness of ≥ 3.0 mm

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