Laboratory Services

Sequential Maternal Screening, Part 2, Serum

Print this page

Updated Test Information:

Test Description
Sequential Maternal Screening, Part 2, Serum

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

Test ID
General Information

Useful for:

  • Prenatal screening for Down syndrome, neural tube defects, and trisomy 18

  • Identifying abnormal levels of alpha-fetoprotein in the second trimester

Testing algorithm:

Specimen Type


Specimen Requirements

Preferred: SST
Red top

Specimen Collection / Processing Instructions

  • Collect blood between 15 weeks, 0 days and 22 weeks, 6 days

  • Do not collect blood after performing amniocentesis, as that may lead to an artificially increased serum alpha-fetoprotein level and unreliable results

  • Centrifuge and aliquot within 2 hours of collection.

Required Information

Collection date is required


  • Refrigerated (preferred): 7 days

  • Ambient: 7 days

  • Frozen: 90 days

Unacceptable Specimen Conditions

Gross hemolysis


  • 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 screenpositive 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

  • Maternal serum alpha-fetoprotein (AFP) should not be measured after amniocentesis because maternal-fetal transfusion may occur, which would falsely increase the serum AFP

  • 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 a small percentage of samples, there is potential for alkaline phosphatase associated positive interference in the Beckman Access uE3 assay. This potential interference does not appear to be related to the amount of alkaline phosphatase in the patient sample. A falsely elevated unconjugated estriol (uE3)test result can lead to inaccurately underestimating the relative risk of chromosomal abnormalities, such as trisomy 21 and 18


Immunoenzymatic Assay

Estimated TAT

1-3 days

Testing Schedule


Test Includes

9 months

CPT Code(s)

81511; 82105 (if appropriate); 82677 (if appropriate); 84702 (if appropriate); 86336 (if appropriate)

Additional Information
Minimum Sample Volume

0.5 mL

Reference Range

An interpretive report will be provided

Performing Lab


LOINC Code(s)

43995-0, 49092-0, 43995-0, 49090-4, 43994-3, 49091-2, 49035-9, 49035-9, 49035-9, 49035-9, 48407-1, 76348-2, 20450-3, 23811-3, 23811-3, 20466-9, 21264-7, 83086-9, 23841-0, 35738-4, 36904-1, 49092-0, 80615-8, 48767-8, 33882-2, 33882-2, 21112-8, 43993-5, 294