Nuchal translucency (NT) is a fluid-filled space normally seen behind the fetal neck on ultrasound performed in the first trimester of pregnancy
A precise measurement of this space is used in first trimester aneuploidy screening in combination with levels of maternal serum markers [free or total hCG and pregnancy-associated plasma protein A (PAPP-A)] to provide an adjusted risk for fetal aneuploidy
Measurements should be performed between 11w0d and 13w6d weeks of pregnancy
ISPD suggests 12 weeks may be superior because
Patient scheduling may be easier and fetal anatomic visualization is better compared to 11 weeks
Screening performance is superior compared to 13 weeks
Determination of whether or not a measurement is normal requires an accurate measurement of fetal size using a crown rump length (CRL) measurement
Programs exist for credentialing purposes to provide education and ongoing mechanism for quality review and is a necessary requirement for optimal screening performance
A fetal measurement >3.0 mm is an independent risk factor for fetal abnormalities and requires referral and further follow up
More commonly associated with aneuploidies such as Down syndrome and Turner syndrome, but may also be associated with other genetic syndromes, such as skeletal dysplasias
Larger NT may be associated with Noonan syndrome, especially in the context of other structural anomalies such as cardiac and renal findings
Approximately 10% risk with NT >3.0 mm and normal chromosomal complement
Fetal structural anomalies, including cardiac, abdominal wall and diaphragmatic defects, must be assessed by anatomical fetal ultrasound and fetal echocardiography
If the NT is sufficiently large to extend the length of the fetus with visible septations, this is called a ‘cystic hygroma’ and risk of aneuploidy is 50%
Other genetic syndromes and structural anomalies may be present even in those with normal karyotype
normal outcome may be <20%
Refer for high risk OB consultation and genetic counseling, and consider prenatal diagnostic testing
ACOG guidance recommends offering invasive testing using microarray in the setting of fetal structural anomalies seen on prenatal ultrasound
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