Introduction
The triple marker test is a blood test that is performed during pregnancy and involves both screening and diagnostic aspects. It is not a straightforward diagnostic test and only serves as an indicator of potential genetic abnormalities in the fetus. Additional tests and consultations with a doctor are necessary to confirm any suspected abnormalities. Moreover, the triple marker test report takes into account various factors such as age, weight, ethnicity, pre-existing medical conditions, and the type of pregnancy (for example, multiples or twins) of the expectant mother.
What Are the Indications to Perform This Test?
During gestational weeks 15 to 20, a blood test known as the "triple marker test" is performed to detect potential abnormalities in the fetus. This test is typically conducted if the results of the double marker test are inconclusive or if the expectant mother presents certain risk factors such as family history of genetic problems, being 35 years of age or older, having diabetes and taking insulin, experiencing prenatal viral infections, exposure to radiation, or taking medication with significant side effects.
In the second trimester, healthcare providers may recommend the triple marker test to analyze the levels of three hormones in the serum, namely: alpha-fetoprotein (AFP), unconjugated estriol, and human chorionic gonadotropin (beta-hCG).
Which Hormones Are Tested in the Triple Marker Test?
1. Alpha-Fetoprotein (AFP): It is a substance generated by the fetus, and elevated levels in the mother's blood may indicate the presence of a neural tube defect in the developing baby, such as spina bifida (a congenital condition affecting the spinal cord and usually apparent at birth) or anencephaly (a severe congenital condition characterized by the absence of a significant portion of the skull and cerebral hemispheres of the brain).However, the most common cause of high AFP levels is inaccuracy in dating the pregnancy. On the other hand, low levels of AFP and abnormal levels of hCG and estriol can indicate the presence of chromosome abnormalities, such as Trisomy 21 (Down syndrome) or Trisomy 18 (Edwards syndrome), in the developing fetus.
Although the primary aim of the test is to screen for genetic disorders, the triple-screen results can also be used to detect:
- Pregnancies.
- Pregnancies that are either more or less advanced than expected.
2. Estriol: It is present in both the fetus and placenta. If the levels of estriol are low, it suggests that the baby has a higher risk of being born with Down syndrome. The risk increases further if the AFP levels are low and the hCG levels are high.
3. Human Chorionic Gonadotropin (hCG): The placenta produces hCG. Low levels of this hormone may indicate ectopic pregnancies or miscarriages. Conversely, high levels of hCG could signify molar pregnancies or multiple pregnancies.
What Is the Procedure of Triple Marker Test?
The procedure for a triple marker test is similar to a blood test. After cleaning the skin, a needle is inserted to draw blood, which is then sent to the laboratory for analysis. A rubber band may be used to make the vein more accessible.
What Does the Triple Marker Test Result Mean?
The triple test is a screening test. Its results only suggest the possibility of the mother carrying a baby with a genetic disorder. However, the test has a high incidence of false-positive results. Thus, abnormal results require additional testing to arrive at a diagnosis. Doctors consider various factors that may affect the test results, such as the mother's age, weight, ethnicity, and whether she is diabetic or carrying multiple fetuses.
What Are the Recommended Actions After Getting the Triple Marker Test Results?
The triple marker test can yield false-positive results, indicating a potential issue where none exists. Therefore, reviewing the test results with a healthcare provider who can interpret them accurately is crucial.
In order to minimize the risk of misdiagnosis, a more conservative approach might involve conducting a second triple-screen test, followed by a high-definition ultrasound. A more invasive procedure, such as amniocentesis, might be recommended if the results remain abnormal.
If the triple marker test indicates high levels of AFP, the doctor may order a detailed ultrasound to examine the fetal skull and spine for neural tube defects. Ultrasound imaging can also determine the age of the fetus and the number of fetuses a woman is carrying.
What Is the Difference Between the Double Marker Test and the Triple Marker Test?
During pregnancy, various screening tests are performed to detect any possible genetic abnormalities in the fetus. The double marker test and the triple marker test are two such screening tests that are commonly used. Both tests help to detect the risk of certain chromosomal disorders in the fetus. However, there are some differences between these tests.
-
Number of Markers: The double marker test uses two markers - human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein-A (PAPP-A) - to assess the risk of Down syndrome and other chromosomal abnormalities. The triple marker test, on the other hand, uses three markers - alpha-fetoprotein (AFP), hCG, and unconjugated estriol (uE3) - to assess the risk of Down syndrome, neural tube defects, and other chromosomal abnormalities.
-
Timing: The double marker test is usually performed between eight and 14 weeks of pregnancy, while the triple marker test is performed between 15 and 20 weeks of pregnancy.
-
Accuracy: The triple marker test is more accurate than the double marker test in detecting chromosomal abnormalities. The triple marker test has a higher sensitivity, meaning it can detect more cases of chromosomal abnormalities than the double marker test.
-
False Positive Rate: The double marker test has a higher false positive rate than the triple marker test. This means that more women may receive a positive result on the double marker test, indicating a higher risk of chromosomal abnormalities when, in fact, their fetus is healthy. The triple marker test has a lower false positive rate, which means that fewer women may receive a positive result when their fetus is actually healthy.
-
Cost: The double marker test is generally less expensive than the triple marker test.
Conclusion
The triple marker test is a pregnancy screening test that checks for genetic abnormalities in the fetus by analyzing three hormones in the mother's blood. It is recommended for high-risk pregnancies or if the results of the double marker test are unclear. However, it is not a diagnostic test, and further testing and consultations with a healthcare provider are needed to confirm any abnormalities. False positives are common, and additional testing may be required if abnormalities are suspected.
