Management of Increased Nuchal Translucency in Fetuses

Definition and Clinical Significance

The American College of Radiology states that a fetus with increased nuchal translucency (NT ≥3 mm) requires immediate genetic counseling, invasive diagnostic testing, and comprehensive follow-up monitoring due to significant risks of chromosomal abnormalities, structural defects, and adverse pregnancy outcomes 1, 2
Nuchal translucency is the hypoechoic space between the overlying skin and underlying soft tissues of the posterior cervical spine in the first-trimester fetus, and its measurement increases with crown-rump length, so gestational age must be considered when determining if a measurement is abnormal 2
An increased NT is defined as ≥3 mm or above the 99th percentile for the crown-rump length, and approximately one-third of fetuses with NT ≥3 mm will have chromosomal abnormalities, with half of these being trisomy 21 2, 3

About one-third of fetuses with NT thickness above 3 mm will have a chromosomal abnormality, according to the American College of Radiology 3, 4
The risk of adverse pregnancy outcomes increases proportionally with the degree of NT enlargement, as stated by the American College of Radiology 1, 5

In euploid fetuses with increased NT, there remains an elevated risk of structural anomalies, particularly cardiac defects, as reported by the American College of Radiology 1, 2
The risk of major structural anomalies persists even in fetuses subsequently found to be euploid, according to the American College of Radiology 6, 5

In euploid fetuses with NT ≥3 mm, 10% have genetic variants consistent with Noonan syndrome, as stated by the American College of Radiology 1, 3
Cell-free fetal DNA screening only detects trisomy 21, 18, 13, and sex chromosome aneuploidies, but will miss other genetic causes of increased NT such as Noonan syndrome and 22q11.2 deletion syndrome, as reported by the American College of Radiology 1, 9

Genetic counseling and invasive diagnostic testing should be promptly offered, as recommended by the American College of Radiology 3, 2
Consider cell-free fetal DNA screening, supported by the American College of Obstetricians and Gynecologists (ACOG) for women with NT ≥3 mm 1, 9
Perform targeted genetic studies, including microarray analysis, which is recommended in all cases of increased NT by the American College of Radiology 1, 3

Early fetal anatomic survey can be performed at the time increased NT is identified, providing opportunity for early detection of major malformations, as stated by the American College of Radiology 1, 5
Second trimester anatomic survey should be offered regardless of fetal DNA analysis results, as recommended by the American College of Radiology 1, 6
Fetal echocardiography is an accepted indication for NT ≥3 mm, with optimal timing at 18-22 weeks of gestation, as reported by the American College of Radiology 7, 8

Serial fetal surveillance should be added to routine prenatal care, with periodic ultrasound examinations to monitor fetal growth and well-being, as recommended by the American College of Radiology 1, 5