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Triple Screening Test: A Comprehensive Review​

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The Triple Screening Test (Triple Marker Test) is a prenatal biochemical screening method used during the second trimester of pregnancy to assess the risk of specific chromosomal abnormalities and neural tube defects in the fetus. Although it does not provide a definitive diagnosis, it plays a significant role in identifying pregnancies at increased risk and guiding further diagnostic evaluation. This article provides a comprehensive overview of the components, timing, clinical indications, interpretation, accuracy, advantages, and limitations of the Triple Screening Test.

1. Introduction​

Prenatal screening aims to identify pregnancies at increased risk for fetal anomalies, allowing informed decision-making and appropriate clinical management. The Triple Screening Test is one of the traditional second-trimester screening tools and has been widely used, particularly in settings where advanced screening methods may not be readily available.

2. Definition of the Triple Screening Test​

The Triple Screening Test is a maternal serum screening test that measures three biochemical markers in maternal blood:

• Alpha-fetoprotein (AFP)
• Human chorionic gonadotropin (hCG)
• Unconjugated estriol (uE3)

The measured values are combined with maternal demographic and clinical factors to estimate the risk of fetal chromosomal abnormalities and neural tube defects.

3. Timing of the Test​

The Triple Screening Test is optimally performed between 16 and 18 weeks of gestation, although it may be conducted between 15 and 20 weeks. Accurate gestational dating is essential for correct interpretation of results.

4. Biochemical Markers and Their Significance​

4.1 Alpha-Fetoprotein (AFP)​

AFP is a glycoprotein produced primarily by the fetal liver. Abnormally elevated maternal serum AFP levels are associated with open neural tube defects, such as spina bifida and anencephaly, while decreased levels may be associated with chromosomal abnormalities.

4.2 Human Chorionic Gonadotropin (hCG)​

hCG is produced by the placenta and plays a critical role in maintaining pregnancy. Elevated hCG levels are commonly associated with Down syndrome, whereas reduced levels may suggest Edwards syndrome (Trisomy 18).

4.3 Unconjugated Estriol (uE3)​

uE3 is synthesized by the placenta from fetal adrenal precursors. Low levels are associated with chromosomal abnormalities, including Down syndrome and Trisomy 18.

5. Conditions Screened by the Triple Test​

5.1 Down Syndrome (Trisomy 21)​

Typical biochemical pattern:

• AFP: decreased
• hCG: increased
• uE3: decreased

5.2 Edwards Syndrome (Trisomy 18)​

Typical biochemical pattern:

• AFP: decreased
• hCG: decreased
• uE3: decreased

5.3 Neural Tube Defects​

• AFP: increased

6. Interpretation of Results​

Results are reported as risk ratios (e.g., 1:250, 1:1000) rather than as positive or negative findings. A commonly used cutoff for increased risk of Down syndrome is 1:250. Importantly, a high-risk result does not confirm the presence of a fetal abnormality but indicates the need for further evaluation.

7. Accuracy and Clinical Performance​

The detection rate of the Triple Screening Test for Down syndrome is approximately 65–70%, with a false-positive rate of about 5%. Its sensitivity is lower than that of first-trimester combined screening or non-invasive prenatal testing (NIPT).

8. Follow-Up After High-Risk Results​

If an increased risk is identified, additional diagnostic or screening methods may be recommended, including:

• Detailed (level II) ultrasonography
• Non-invasive prenatal testing (cell-free fetal DNA analysis)
• Amniocentesis (definitive diagnostic test)

9. Advantages of the Triple Screening Test​

• Non-invasive and safe for both mother and fetus
• Relatively low cost
• Widely available
• Useful when first-trimester screening was missed

10. Limitations​

• Does not provide a definitive diagnosis
• Lower sensitivity compared to newer screening methods
• Results influenced by maternal age, weight, diabetes, smoking, and gestational age errors
• Higher false-positive rates than advanced screening tests

11. Current Clinical Role​

With the increasing use of first-trimester combined screening and NIPT, the Triple Screening Test is now primarily used in cases where earlier screening was not performed or where access to advanced testing is limited.

12. Conclusion​

The Triple Screening Test remains a valuable prenatal screening tool in selected clinical contexts. While it has limitations in sensitivity and specificity, it continues to play an important role in prenatal care by identifying pregnancies that may benefit from further diagnostic evaluation.