Dual Marker Test
What is Dual Marker Test?
Dual marker test is also known as Double Marker Test. This test measures the levels of b-hCG and Pregnancy Associated Plasma Protein (PAPP-A) in blood. It is generally advised for women who are above the age of 35 years as they fall in risk of delivering a baby with Down’s syndrome. Apart from that, it is advised for younger women as well. This test helps in screening the fetus for any abnormalities before birth. It is done from 9 to 13 weeks of pregnancy.
Why is Dual Marker Test done?
To detect Down’s syndrome
To detect Trisomy 18
Ladies having a family history of any of these syndromes
What does Dual Marker Test Measure?
This test measures the levels of b-hCG and PAPP-A in blood with the ultrasound test. b-hCG is a hormone which is produced by the cells in the developing placenta during pregnancy. The levels of b-hCG increases in early pregnancy. The role of b-hCG in early pregnancy is to maintain the function of corpus luteum (the hormone-secreting structure that develops in an ovary). During the first three weeks production of b-hCG increases reaching to peak levels at 10th week (from the last menstrual cycle). After that, the levels of b-hCG start to fall to negligible within a few weeks after delivery.
PAPP-A is secreted by the placenta and its levels increase with duration of pregnancy. Variety of tissues express PAPP-A at very lower levels. Plaques which are not stable in coronary arteries also express PAPP-A in high levels.
Dual marker test is done along with Nuchal Translucency test to confirm the diagnosis of any genetic abnormality.
Nuchal Translucency (NT) is a measurement of the fluid beneath the skin along the back of the baby's neck. NT is measured by ultrasonography.
Interpreting Dual Marker Test results
All women should be screened for dual marker test in pregnancy for any pre-birth abnormalities irrespective of age. The ideal duration of this test is between 10-13 weeks of pregnancy. But it can be done between 9-13 weeks of pregnancy.