Quad Screen Risk Calculator

Enter your AFP, hCG, estriol, and inhibin A MoM values along with your maternal age to estimate Down syndrome and neural tube defect risk from your quad screen results.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter AFP MoM
Input the AFP multiple of median value from your quad screen report, typically ranging from 0.5 to 2.5 MoM.
2
Enter hCG MoM
Provide the hCG multiple of median, usually between 0.5 and 2.5 MoM, as indicated on your lab results.
3
Enter Estriol (uE3) MoM
Input your unconjugated estriol multiple of median, which commonly falls between 0.5 and 2.0 MoM.
4
Enter Inhibin A MoM
Add your Inhibin A multiple of median, generally within 0.5 to 2.0 MoM. Elevated levels can be a marker for certain conditions.
5
Enter Maternal Age
Input your age at the expected date of delivery, as age is a significant factor in baseline chromosomal risk.
6
Review Your Results
The calculator will display your estimated risk for Down syndrome and neural tube defects, along with individual marker statuses and recommended next steps.

Example Calculation

A 30-year-old expectant parent receives quad screen results with all marker MoM values within the typical range.

AFP MoM

1.0

hCG MoM

1.0

Estriol (uE3) MoM

1.0

Inhibin A MoM

1.0

Maternal Age (yrs)

Results

900

Tips

Consider the Screening Window

The quad screen is most accurate when performed between 15 and 20 weeks of gestation. Results outside this window might be less reliable; discuss timing with your healthcare provider.

Understand 'Screen Positive' vs. Diagnosis

A 'screen positive' result, indicating a higher risk, does not mean your baby has a condition. It merely suggests further diagnostic testing, such as NIPT or amniocentesis, may be warranted.

Factor in Maternal Age Trends

While a 30-year-old has a baseline Down syndrome risk of approximately 1 in 900, this naturally increases with age, reaching around 1 in 385 at age 35 and 1 in 100 by age 40, making marker interpretation even more critical for older parents.

Estimating Fetal Health Risks with the Quad Screen

The Quad Screen Risk Calculator helps interpret the results of a prenatal screening test, providing an estimated risk for Down syndrome (Trisomy 21) and neural tube defects. This crucial tool aids expectant parents and healthcare providers in evaluating the likelihood of these conditions based on maternal age and four specific blood markers: AFP, hCG, unconjugated estriol, and inhibin A. For instance, a 30-year-old with typical marker levels might have a Down syndrome risk of around 1 in 900, a figure that becomes more precise with the calculator's pattern analysis. This information, especially in 2025, is vital for guiding further diagnostic decisions.

Understanding Your Quad Screen Results

The quad screen is a valuable second-trimester screening tool, but interpreting its results requires careful consideration. The test measures specific biomarkers, and their levels are compared to typical ranges for a given gestational age. A "screen positive" result doesn't mean a diagnosis; rather, it indicates an elevated risk that warrants further investigation. Conversely, a "screen negative" suggests a lower risk, but does not guarantee the absence of a condition. For example, low AFP levels, high hCG, and low estriol are often associated with an increased risk of Down syndrome, while very high AFP levels can signal a neural tube defect.

The Calculation Behind Quad Screen Risk Assessment

The Quad Screen Risk Calculator employs a pattern-based scoring system and likelihood ratios to adjust a maternal age-based baseline risk. It assesses deviations in four key markers: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin A.

The primary formula involves:

adjusted risk = baseline risk × likelihood ratio

where:

baseline risk is the age-specific risk for Trisomy 21.
likelihood ratio is a multiplier derived from the specific pattern of the four marker MoM values.

Each marker's deviation from the median contributes a specific factor to the overall likelihood ratio, which is then applied to the maternal age-based risk to provide a personalized estimate.

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Assessing a Routine Quad Screen Scenario

Consider an expectant parent, aged 30, whose quad screen results show all marker multiples of the median (MoM) at 1.0. This scenario typically represents a low-risk profile.

Input AFP MoM: 1.0
Input hCG MoM: 1.0
Input Estriol (uE3) MoM: 1.0
Input Inhibin A MoM: 1.0
Input Maternal Age: 30 years

Given these inputs, the calculator first determines that all marker levels are within their normal ranges, resulting in a low likelihood ratio (LR = 1.0). The age-based baseline risk for Down syndrome at 30 years is approximately 1 in 900. When the LR is applied to this baseline, the adjusted risk remains 1 in 900. This indicates a "Screen Negative — Low Risk" outcome for Down syndrome, with a low risk for neural tube defects.

💡 To ensure overall maternal health during pregnancy, our Calcium Needs in Pregnancy Calculator can help you assess dietary requirements, complementing your prenatal care.

Understanding Your Quad Screen Results

A quad screen is a powerful screening tool for identifying pregnancies at increased risk for certain conditions, but it is not a diagnostic test. A 'screen positive' result, for example, means the statistical chance of a condition like Down syndrome is higher than a predetermined cutoff, often 1 in 270. This threshold is set by clinical guidelines, such as those from the American College of Obstetricians and Gynecologists (ACOG), to balance detection rates with false positives. If the AFP MoM is significantly elevated (e.g., above 2.5), it specifically flags an increased risk for neural tube defects, prompting further investigation through a high-resolution ultrasound. Always consult a healthcare provider, such as an obstetrician or genetic counselor, to interpret your specific results and discuss personalized next steps.

How Obstetricians Interpret Quad Screen Outcomes

Obstetricians and genetic counselors utilize quad screen results as a critical component of a comprehensive prenatal risk assessment, not as a standalone diagnosis. They look beyond a simple "positive" or "negative" to understand the specific pattern of MoM values and how it integrates with maternal age and medical history. For instance, a very low AFP, high hCG, and low estriol pattern strongly points towards Trisomy 21, even if the overall risk is still below 1 in 100. They also consider the gestational age accuracy; a miscalculated due date can skew MoM values, potentially leading to a false positive or negative. A "concerning" result (e.g., a risk greater than 1 in 250 for Down syndrome) typically triggers a recommendation for non-invasive prenatal testing (NIPT) or diagnostic procedures like amniocentesis, allowing the parents to make informed decisions based on confirmed information.

Frequently Asked Questions

What is a Quad Screen and what does it test for?

A quad screen is a prenatal blood test performed during the second trimester of pregnancy, typically between 15 and 20 weeks. It measures four specific substances in the mother's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin A. The test estimates the risk of the fetus having certain chromosomal abnormalities, specifically Down syndrome (Trisomy 21), and neural tube defects.

What do MoM values mean in a Quad Screen report?

MoM stands for 'Multiple of the Median,' which is a standard way to express the concentration of a substance in maternal blood relative to the median concentration found in unaffected pregnancies at the same gestational age. For example, an AFP MoM of 1.0 means the AFP level is exactly at the median, while an MoM of 2.0 means it's twice the median. Deviations from the normal range (typically 0.5 to 2.5 MoM) can indicate an increased risk for certain conditions.

What are the next steps if my Quad Screen result is 'Screen Positive'?

If your quad screen result is 'Screen Positive,' indicating an increased risk, your healthcare provider will typically recommend further evaluation. This may include non-invasive prenatal testing (NIPT), which analyzes fetal DNA in the mother's blood, or more definitive diagnostic procedures like amniocentesis or chorionic villus sampling (CVS). It's crucial to consult with a genetic counselor to understand these options and make informed decisions about your pregnancy care.

How accurate is the Quad Screen Risk Calculator?

The Quad Screen Risk Calculator provides an estimated risk based on the input MoM values and maternal age, reflecting the statistical likelihood of certain conditions. It is a screening tool, not a diagnostic one, meaning it identifies pregnancies at higher risk that may warrant further testing rather than definitively diagnosing a condition. The overall detection rate for Down syndrome with the quad screen is approximately 81% with a false positive rate of about 5%, according to the American College of Obstetricians and Gynecologists (ACOG).