Triple marker test
The triple marker test analyzes how likely an unborn baby is to have certain genetic disorders. It is also known as a multiple Marker test. The exam measures the levels of three important substances in the placenta: alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), and Estriol.
- AFP Test (Alpha Fetoprotein) : AFP is a protein that is produced by the fetus. High levels of this protein are indicative of potential neural tube defects or defects in the fetus’s abdomen.
- HCG (Human Chorionic Gonadotropin) : HCG is a hormone that is secreted by the placenta. Low levels of HCG are seen in miscarriage or ectopic pregnancy. High levels are seen in molar pregnancy or twin/multiple pregnancies.
- Estriol : It is an estrogen that is secreted by the placenta and the fetus. Low levels may indicate the risk of the baby having Downs syndrome.
Triple marker screening is administered as a blood test for women who are between 15 and 20 weeks pregnant. An alternative to this test is the quadruple marker screen test, which also looks at Inhibin A.
A Triple marker screen test takes a sample of blood and detects the levels of AFP, HCG, and Estriol in it. Abnormal levels of these substances may indicate the presence of:
- Down’s syndrome
- Edwards syndrome
- Neural tube defects (such as spina bifida and anencephaly).
- Multiple infants
- An improper timeline (the pregnancy is further along or not as far along as once thought)
For whom is the Triple Marker Test is the most important?
This is a screening test and it gives an idea to the expectant parents about the chances of their baby having genetic diseases or chromosomal abnormality. The placenta that nourishes the baby in the womb secretes these substances which are detectable in the mother’s blood. This test is of utmost importance in the following cases:
- Pregnant women above the age of 35 who are at a greater risk for pregnancy complications
- Viral infection during pregnancy
- Family history of birth defects
- History of a similar defect in baby in the previous pregnancy
- History of exposure to radiation in any form
- Ladies having diabetes or on insulin treatment
Interpretation of the Triple Marker Test
The results of the triple marker test are interpreted on the basis of the following factors. The final result gives a probability in the form of a ratio of the fetus having a chromosomal defect. If the probability or risk ratio is high, then further testing needs to be carried out.
- Mother’s age
- Weight of the mother
- Presence of diabetes
- Single or multiple pregnancies
- Number of weeks of pregnancy
If the risk ratio is low there is nothing to worry about. In case there is a high risk ratio, then further testing like amniocentesis needs to be done. Amniocentesis is testing of the amniotic fluid by drawing the fluid under ultrasound guidance.
In case the AFP levels are high, then the doctor will check by using an ultrasound for the baby’s skull and spine for neural tube defects. If the AFP levels are low with high HCG, Down’s syndrome is to be suspected. In such cases, NT scan or Nuchal Translucency scan is very important where the presence of the nasal bone is checked and the amount of fluid at the back of the baby’s neck is measured. Both these parameters combined with the results of the triple test give a fair risk ratio or probability of the presence of chromosomal abnormalities in the baby.