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HelpTest ID SEQA Sequential Maternal Screening, Part 1, Serum
Ordering Guidance
When part 1 is negative, part 2 must be completed in order to receive an interpretable result. If collecting a second-trimester specimen is expected to be difficult, order first-trimester screening instead (1STT1 / First Trimester Maternal Screen, Serum).
If a stand-alone neural tube defect risk assessment is desired, order MAFP1 / Alpha-Fetoprotein (AFP), Single Marker Screen, Maternal, Serum.
Additional Testing Requirements
Sequential maternal screening is a 2-part test that includes a first-trimester sample (this test) and a second-trimester sample (SEQB / Sequential Maternal Screening, Part 2, Serum).
Necessary Information
Approval to send specimen for first-trimester screening is required and may take up to 5 business days to complete. Nuchal translucency (NT) measurements are only accepted from NT-certified sonographers. Do not send specimen to Mayo Clinic Laboratories if the sonographer is not NT-certified or before completing the application process. See Maternal Screening: Sonographer Approval Process. Complete the NT/CRL Data for First Trimester/Sequential Maternal Screening.
Specimen Required
Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions:
1. The ultrasound and blood draw must be completed within a gestational window of 10 weeks, 0 days and 13 weeks, 6 days, which corresponds to a crown-rump length range of 31 to 80 mm.
2. Centrifuge and aliquot serum into a plastic vial within 2 hours of collection.
Forms
First Trimester/Sequential Maternal Screening Patient Information (T593) is required.
Secondary ID
113398Useful For
First-trimester prenatal screening for trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome)
Testing Algorithm
Sequential maternal screening is a 2-step test, with first- and second-trimester components. It requires a nuchal translucency measurement and blood collection in the first trimester. If the result from part 1 indicates a risk for Down syndrome that is higher than the screen cutoff, the screen is completed, and a report is issued. If the results from part 1 are negative, an additional blood collection in the second trimester is required (SEQB / Sequential Maternal Screening, Part 2, Serum). If the second specimen is not received for sequential screening, the results are uninterpretable, and no maternal risk will be provided.
For additional information see Sequential Maternal Serum Screening Testing Algorithm.
Special Instructions
Method Name
Immunoenzymatic Assay
Reporting Name
Sequential Maternal Screen, Part 1Specimen Type
SerumSpecimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 7 days | |
| Frozen | 90 days | ||
| Ambient | 7 days |
Clinical Information
Maternal serum screening is used to identify pregnancies that may have an increased risk for certain birth defects, such as trisomy 21 (Down syndrome), neural tube defects (NTD) and trisomy 18. Various options for maternal serum screening are available and include: first trimester, second trimester, and cross-trimester. Sequential screening is a type of cross-trimester screening that has an improved detection rate as compared to either first- or second-trimester screening. Sequential screening combines biochemical and ultrasound markers (nuchal translucency: NT) measured in both trimesters of the pregnancy.
This test involves an ultrasound and a blood draw. The ultrasound measurement, referred to as the NT measurement, is difficult to perform accurately. Therefore, NT data is accepted only from NT-certified sonographers. Along with the NT measurement, a maternal serum specimen is collected to measure pregnancy-associated plasma protein A (PAPP-A). The results of the ultrasound measurement and blood work, along with the maternal age and demographic information, are used to calculate trisomy 21 (Down syndrome) and trisomy 18 risk estimates.
If the result from part 1 indicates a risk for Down syndrome that is higher than the screen cutoff, the screen is completed, and a report is issued. In that event, the patient is typically offered counseling and diagnostic testing. When the part 1 screen is completed, NTD risk is not provided. For a stand-alone NTD-risk assessment, order MAFP1 / Alpha-Fetoprotein (AFP), Single Marker Screen, Maternal, Serum.
If the risk from the first trimester is below the established cutoff, an additional serum specimen is collected in the second trimester for SEQB / Sequential Maternal Screen, Part 2, Serum. The blood specimen is tested for AFP, unconjugated estriol , human chorionic gonadotropin , and inhibin A. The information from both trimesters is combined and a report is issued. If results are positive, the patient is typically offered counseling and diagnostic testing.
NT:
The NT measurement, an ultrasound marker, is obtained by measuring the fluid-filled space within the nuchal region (back of the neck) of the fetus. While fetal NT measurements obtained by ultrasonography increase in normal pregnancies with advancing gestational age, Down syndrome and trisomy 18 fetuses have larger NT measurements than gestational age-matched normal fetuses. Increased fetal NT measurements can therefore serve as an indicator of an increased risk for Down syndrome and trisomy 18.
PAPP-A:
PAPP-A is a 187-kDa protein comprised of 4 subunits: 2 PAPP-A subunits and 2 pro-major basic protein subunits. PAPP-A is a metalloproteinase that cleaves insulin-like growth factor-binding protein-4 (IGFBP-4), dramatically reducing IGFBP-4 affinity for IGF1 and IGF2, thereby regulating the availability of these growth factors at the tissue level. PAPP-A is highly expressed in first-trimester trophoblasts, participating in regulation of fetal growth. Levels in maternal serum increase throughout pregnancy. Low PAPP-A levels before the fourteenth week of gestation are associated with an increased risk for Down syndrome and trisomy 18.
Reference Values
An interpretive report will be provided.
Cautions
Nuchal translucency (NT) measurements must be obtained from NT-certified sonographers. NT-measurement quality indicators will be monitored on a regular basis. Sonographers will be contacted if there is ongoing deviation in the quality indicators.
Incorrect or incomplete information may significantly alter results.
A screen-negative result does not guarantee the absence of fetal defects. A screen-positive result does not provide a diagnosis but indicates that further diagnostic testing should be considered (an unaffected fetus may have screen-positive result for unknown reasons). In fact, given the low prevalence of Down syndrome, the majority of women with a positive screen will not have a Down syndrome fetus.
In twin pregnancies, the risk for Down syndrome is approximated, using twin-adjusted medians. In cases where one twin has demised, results may be unreliable.
Results are not available for triplets or higher-multiple pregnancies.
Each center offering maternal serum screening to patients should establish a standard screening protocol, which provides pre- and post-screening education and appropriate follow-up for screen-positive results.
In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results and the laboratory should be alerted if the result does not correlate with the clinical presentation.
Day(s) Performed
Monday through Friday
Report Available
4 to 6 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
84163