Laboratory Services

Sequential Maternal Screening, Part 1, Serum

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Updated Test Information:

Test Description
Sequential Maternal Screening, Part 1, Serum

Maternal Serum Sequential Screen; Sequential Screening; Serum Stepwise Sequential Screen; Stepwise Maternal Screen; Stepwise Sequential

Test ID
General Information

Useful for:

  • First-trimester prenatal screening for Down syndrome (trisomy 21) and trisomy 18

Testing algorithm:

  • Sequential maternal screening is a 2-step test, with first- and second-trimester components

  • A nuchal translucency (NT) 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 (see 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

    • If collecting a secondtrimester specimen is expected to be difficult, order first-trimester screening instead (see 1STT1: First Trimester Maternal Screen, Serum)

  • See Sequential Maternal Serum Screening Testing Process

  • See also Prenatal Aneuploidy Screening and Diagnostic Testing Options

Specimen Type


Specimen Requirements

Preferred: SST
Red top

Specimen Collection / Processing Instructions

  • 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 (CRL) range of 31 to 80 mm

  • Centrifuge and aliquot serum within 2 hours of collection

Required Information

  • Refrigerated (preferred): 7 days

  • Ambient: 7 days

  • Frozen: 90 days

Unacceptable Specimen Conditions

Gross hemolysis


  • 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


Immunoenzymatic Assay

Estimated TAT

1-3 days

Testing Schedule


Test Includes

9 months

CPT Code(s)


Additional Information
Minimum Sample Volume

0.5 mL

Reference Range

An interpretive report will be provided

Performing Lab


LOINC Code(s)

43995-0, 50679-0, 43995-0, 49090-4, 43994-3, 48407-1, 76348-2, 33069-6, 49035-9, 33069-6, 49035-9, 49586-1, 80615-8, 48767-8, 33882-2, 21112-8, 43993-5, 29463-7, 29463-7, 33248-6, 32624-9, 72166-2, 34970-4, 11957-8, 11957-8, 11888-5, 11878-6, 92568-5, 472