The Double Marker Test is a non-invasive prenatal screening performed during the first trimester of pregnancy. It assesses the potential risk of certain chromosomal abnormalities in the developing baby. This test provides information that can guide further medical decisions.
Purpose of the Double Marker Test
The primary purpose of the Double Marker Test is to screen for the likelihood of chromosomal conditions, particularly Down syndrome (Trisomy 21) and Edward syndrome (Trisomy 18). These conditions arise from an abnormal number of chromosomes, specifically an extra copy of chromosome 21 or 18. The test can also indicate risk for Patau syndrome (Trisomy 13).
This test measures the levels of two substances in the pregnant person’s blood: free beta-human chorionic gonadotropin (free beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A). Altered levels of these markers can suggest an increased risk for these genetic conditions. This test assesses risk rather than providing a definitive diagnosis of a chromosomal abnormality.
How the Test is Conducted
The Double Marker Test is performed during the first trimester of pregnancy, between the 10th and 13th weeks. This timeframe is chosen for optimal accuracy. The procedure involves collecting a small blood sample from the expectant parent’s arm.
No special preparation, such as fasting, is required before the test. The blood sample is sent to a laboratory for analysis of free beta-hCG and PAPP-A levels. For a more comprehensive risk assessment, the Double Marker Test results are combined with a Nuchal Translucency (NT) scan. The NT scan measures the fluid at the back of the baby’s neck, and these measurements, along with the blood test results, contribute to the overall risk calculation.
Understanding Your Results
Results from the Double Marker Test are presented as a risk ratio, indicating the probability of a chromosomal abnormality. For instance, a result might be expressed as 1:1000, meaning there is a 1 in 1000 chance that the baby has the screened condition. These results are categorized as either “low risk” or “high risk.”
A “low risk” or “screen-negative” result suggests a reduced probability of chromosomal abnormalities, and no further immediate testing is recommended. Conversely, a “high risk” or “screen-positive” result indicates an elevated chance of a genetic condition. However, a high-risk result does not confirm that the baby has the condition; it only signifies a higher statistical probability.
Several factors contribute to the calculation of this risk, including maternal age, gestational age, and the measured levels of free beta-hCG and PAPP-A. If an NT scan was performed, its measurements are also integrated into this risk assessment. Accurate gestational dating is important, as incorrect dating can affect the risk calculation.
What Happens After the Double Marker Test
For individuals who receive a low-risk result from the Double Marker Test, no further action is needed regarding the conditions screened for. This outcome provides reassurance during pregnancy. However, a low-risk result does not eliminate the possibility of all potential issues, as the test screens for specific chromosomal conditions, not all possible birth defects.
If the Double Marker Test indicates a high-risk result, healthcare providers will discuss options for further diagnostic testing. These diagnostic tests, such as chorionic villus sampling (CVS) or amniocentesis, can provide a definitive diagnosis of chromosomal abnormalities. These diagnostic procedures are invasive and carry a small risk of complications, including miscarriage.
The Double Marker Test is a screening tool, designed to identify pregnancies that may benefit from additional evaluation, rather than a diagnostic one. This distinction is important because a positive screening result does not equate to a diagnosis. There is also a possibility of false positives, where the test suggests a risk when none exists, or false negatives, where a condition is present but not indicated by the screening.