The dual marker test is a prenatal screening that measures two biochemical markers—Free Beta Human Chorionic Gonadotropin (Free β-hCG) and Pregnancy-Associated Plasma Protein A (PAPP-A)—in the mother’s blood. This test is generally done between the 10th and 14th weeks of pregnancy, and it helps assess the risk of chromosomal abnormalities in the fetus, such as Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18).
Markers Explained
- Free Beta hCG: Free β-hCG is a hormone produced by the placenta shortly after implantation. High levels of Free β-hCG may be associated with an increased risk of chromosomal anomalies like Down syndrome.
- PAPP-A: PAPP-A is a protein produced by the placenta during pregnancy. Low levels of PAPP-A can be indicative of chromosomal disorders, particularly Down syndrome, as well as potential complications like restricted fetal growth or preeclampsia.
How the Dual Marker Test Works
The test combines the levels of Free β-hCG and PAPP-A with maternal factors, such as age and gestational age, to produce a risk ratio. This ratio helps to predict the likelihood of the fetus having a chromosomal abnormality.
Risk Assessment
- Low Risk: A low-risk result suggests that the likelihood of a chromosomal abnormality is low, but it does not guarantee the absence of abnormalities.
- High Risk: A high-risk result does not confirm a chromosomal abnormality; it simply indicates a higher probability, warranting further testing. Additional diagnostic tests, such as chorionic villus sampling (CVS) or amniocentesis, may be recommended to confirm any findings.
Advantages and Limitations
- Advantages: The dual marker test is non-invasive, safe for both mother and fetus, and provides early information that can assist in decision-making.
- Limitations: The test is a screening, not a diagnostic, meaning it cannot provide a definitive diagnosis but rather an assessment of risk. It may also yield false positives or negatives.
Clinical Usefulness
The dual marker test, often combined with an ultrasound nuchal translucency scan, is an essential tool in the first trimester for early risk assessment. When used with additional screenings or diagnostic tests, it provides valuable information for expecting parents and healthcare providers to manage the pregnancy better.