Prenatal screening for Down syndrome and trisomy 18
The first-trimester screen for trisomy 21 and trisomy 18 includes pregnancy-associated plasma protein-A (PAPP-A), total human chorionic gonadotropin (hCG), and nuchal translucency (NT) measurement along with CRL. Analyte values are compared to median values at a given gestational age and multiple of the median (MoM) results obtained. The MoM results are used in a multivariate algorithm that includes the mother’s age to derive risk factors for Down syndrome and trisomy 18. An interpretive report is provided.
This test does not screen for neural tube defects. If risk assessment for neural tube defects is desired, collect specimen between 15 weeks, 0 days, and 22 weeks, 6 days for an AFP single marker screen, MAFP1 / Alpha-Fetoprotein (AFP), Single Marker Screen, Maternal, Serum. QUAD screening (QUAD1 / Quad Screen [Second Trimester] Maternal, Serum) is not recommended following the first-trimester screening.
Approval to send the specimen for first-trimester screening is required and may take up to 5 business days to complete. Nuchal translucency (NT) and CRL measurements are only accepted from certified sonographers.
Preferred: Red top
Acceptable: Yellow Top
Specimen Volume: 2-3 mL
Collection Instructions: Centrifuge and aliquot within 2 hours of collection
- Blood draw and ultrasound must be completed between 10 weeks, 0 days and 13 weeks, 6 days, which corresponds to a crown-rump length (CRL) range of 31 to 80 mm.
- Initial or repeat testing is determined in the laboratory at the time of the report and will be reported accordingly.