General Health

What are Dual, Triple and Quadruple Marker Tests?

Overview

Various tests are performed throughout pregnancy to determine the health of the mother and foetus. In most cases, biomarker tests are used to look for congenital and genetic abnormalities in the foetus. They are often performed to determine if the foetus has Down’s syndrome, a genetic defect that impairs the child’s physiological and psychosocial development.

Dual, triple and quadruple marker tests can be employed for the following:

Trisomy 21 is the most prevalent anomaly that the test can detect (Down syndrome). In addition to Down syndrome, the triple and quadruple screens can detect an increased risk of Turner syndrome, triploidy, trisomy 16 mosaicism, foetal mortality, Smith–Lemli–Opitz syndrome, and steroid sulfatase deficiency.

Certain women are more likely to have a baby with congenital abnormalities, such as

  • Women with a history of birth anomalies in their family
  • Women over the age of 35 who are pregnant
  • Insulin therapy for diabetic women

Dual marker test

This is a screening or blood test performed between the 11th and 13th week of the pregnancy in the first trimester. Along with a Nuchal translucency scan, or NT scan, a dual marker test is performed. The hCG (human chorionic gonadotrophin) and PAPP-A (pregnancy-associated plasma protein) are measured as two indicators in the dual marker test, whereas the NT scan detects the fluid under the skin at the back of the baby’s neck.

The results of both of these tests are used to determine whether the foetus has Down syndrome. The results would signify atypical levels of hCG and PAPP-A, and therefore a higher NT scan value if there had been a risk of Down’s syndrome. The pregnant mother is classified as either screen positive or high risk, or screen negative or low risk, depending on the results.

In India, chromosomal disorders affect about one in every 166 births, with one in every 830 newborns having down’s syndrome. If the risk is minimal, the mother is classified as screen negative. The expectant mother will be advised to have a more extensive test, such as amniocentesis or chorionic villus sampling(CVS (chorionic villus sampling), also referred to as chorionic villus biopsy, is a prenatal test that includes collecting a sample of placental tissue to assess for chromosomal abnormalities and other genetic defects), depending on the outcome.

Triple and quadruple marker test

The triple test, also known as the triple screen, the Kettering test, or Bart’s test, is a pregnancy test that determines if a baby is at high or low risk for chromosomal abnormalities during the second trimester (and neural tube defects).

With a sensitivity of 70% and a false-positive rate of 5%, the Triple Screen assesses AFP, estriol, and beta-hCG levels in the blood. Although it is still widely used in Canada and other countries, in some areas of the United States, it is accompanied by the Quad screen (which provides additional inhibin A to the panel and actual outcomes in an 81 per cent sensitivity and a 5% false-positive rate for detecting Down syndrome when carried at 15–18 weeks of gestational age) and other prenatal diagnosis techniques.

During the second trimester of pregnancy, preferably between the 14th and 20th week, a triple or quadruple marker test is conducted. A quadruple marker test is more sensitive than a triple marker test, and a mother is prescribed to undergo one to determine whether the foetus has any genetic abnormalities. A quadruple marker consists of four blood biomarkers: b-hCG (beta-human chorionic gonadotrophin), AFP (serum alpha-fetoprotein), free estriol (also referred to as unconjugated estriol (uE3)), and Inhibin A. Her hCG levels will be high when she is pregnant with a Down syndrome baby, although her AFP and free estriol levels will below. Depending on the results, the mother will be categorised as high-risk or low-risk.

A positive AFP test indicates a congenital abnormality such as “spina bifida”. That’s usually 2.5 times or more than the “normal” level of AFP expected at that point in pregnancy. A positive AFP test could signify a condition such as Down syndrome or Edwards syndrome.

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Low AFP levels with unusual beta hCG and unconjugated estriol levels could signify that the developing baby has Down syndrome, Edwards syndrome, or another type of chromosome anomaly.

Author

Yash Batra

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