Quadruple Marker Test (Quad Screen)

Overview

The Quadruple Marker Study, also known as the Quad Screen, is a prenatal screening test used to estimate the risk of major chromosomal abnormalities and neural tube defects in a developing fetus. According to the document, this non-invasive blood test measures four essential biochemical markers in the mother’s serum: Alpha-Fetoprotein (AFP), Human Chorionic Gonadotropin (hCG), Unconjugated Estriol (uE3), and Inhibin A (page 2). Each marker originates from a specific fetal or placental source – AFP from the fetal liver, hCG from the placenta, uE3 from both fetal liver and placenta, and Inhibin A from placental trophoblasts (page 3).

The test is performed between 15–20 weeks of pregnancy (page 4) and provides a probability-based assessment, not a definitive diagnosis. It helps identify risks for Down’s syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), Patau syndrome (Trisomy 13), and Neural Tube Defects (page 10). It carries 70% sensitivity with a 5% false-positive rate (page 2), making it an important first-line screening tool in routine antenatal care.

Symptoms

Since the Quad Marker test is a screening procedure, the “symptoms” reflect maternal or fetal indicators that prompt clinicians to recommend the test.

1. High-risk pregnancy indicators

The document suggests screening is especially advised for women who:

1. Have a family history of genetic disorders (page 2)
2. Are 35 years or older (page 5)
3. Have diabetes or are on fertility treatments such as HCG injections (page 9)
4. Conceived through IVF, where donor age must be accounted for (page 9)

2. Abnormal ultrasound findings

The anomaly scan is necessary for interpreting the report (page 4), and clinicians may recommend the Quad Marker when ultrasound indicates:

1. Abnormal fetal growth
2. Structural concerns, such as cardiac or brain anomalies
3. Suspected gestational age mismatch

3. Previous pregnancy complications

A history of miscarriage or chromosomal abnormality is listed as a factor influencing risk assessment (page 9).

Thus, symptoms prompting testing are related to risk elevation, not maternal illness.

Causes

The underlying “causes” relate to the biological and analytical factors measured through the Quad Marker study.

1. Variations in fetal and placental biochemistry

Abnormal levels of AFP, hCG, uE3, and Inhibin A drive the interpretation. The document outlines these patterns (page 15):

1. High AFP → Neural tube defects (e.g., spina bifida, anencephaly)
2. Low AFP + low uE3 + high hCG → Down’s syndrome
3. Low AFP + low uE3 + low hCG → Edwards syndrome
4. High hCG → Down’s, twins, or triploidy
5. High Inhibin A → Down’s syndrome

2. Gestational age discrepancies

Accurate dating—verified via ultrasound—is critical because incorrect gestational age causes misinterpretation (page 6).

3. Maternal physiological factors

Maternal weight, ethnicity, medical history, and medications affect hormone levels (pages 3 & 9), influencing results.

4. Biochemical assay interpretation

Markers are evaluated using Multiples of Median (MoM) (page 13–14), comparing patient values against expected medians for the same gestational age.

Risk Factors

Risk factors fall into two categories: maternal/fetal risks and testing/interpretation-related risks.

Maternal & Fetal Risk Factors

1. Advanced maternal age (page 5)
2. Diabetes or hormonal treatment (e.g., HCG injections) (page 9)
3. Genetic disorder history (page 2)
4. IVF conception, requiring donor age consideration (page 9)
5. Previous abnormal pregnancy outcomes

These factors may alter marker levels or increase the likelihood of chromosomal abnormalities.

Technical & Interpretation Risk Factors

The document lists essential considerations:

1. Results depend on exact gestational age (page 6).
2. Inaccurate ultrasound reduces the sensitivity of the test (page 9).
3. Incomplete patient information—missing weight, LMP, ethnicity—can distort risk calculations (pages 7 & 9).
4. The test offers risk probability, not a definitive diagnosis (pages 5 & 16).
5. False-positive and false-negative outcomes are possible due to biological variation (page 16).

Prevention

Here, “prevention” refers to preventing misinterpretation, unnecessary anxiety, and ensuring reliable screening outcomes.

1. Accurate sample collection & documentation

Collect 3 ml of blood in a plain tube, separate serum quickly, and include essential details such as DOB, weight, LMP, and ultrasound report (page 7).

2. Mandatory anomaly scan correlation

Ultrasound is crucial for confirming gestational age and structural integrity (page 6).

3. Patient counseling

Discuss test purpose, limitations, and implications thoroughly (page 5). Patients must know this is a screening test, not a diagnostic tool (page 16).

4. Follow-up diagnostic tests

If high risk, clinicians may recommend amniocentesis or other invasive tests to confirm abnormalities (pages 5 & 11).

5. Genetic counseling

Essential for understanding the impact of results and preparing parents for potential high-risk pregnancy outcomes (page 6).

6. Clinical correlation

Negative results do not guarantee a completely healthy baby (page 16). Preventive accuracy comes from correlating biochemical markers, maternal factors, and ultrasound findings.