Quad Screen or Quadruple marker is a blood test done during the second trimester (15-20 weeks) of pregnancy to identify some chromosomal abnormalities birth defects in the unborn baby. The Quad screen test is done to evaluate levels of the multiple substances in the women’s blood as mentioned below.
- Human chorionic gonadotropin (hCG); a hormone produced by the placenta
- Alpha-fetoprotein (AFP); a protein produced by the growing baby.
- Inhibin A; a hormone produced by the placenta
- Unconjugated Estriol (UE); a hormone produced by baby's liver and placenta
The levels of the above-mentioned substances keep changing every week, during the pregnancy. Hence, before conducting the test it is essential to know the phase and stage of the pregnancy of the woman. Quad screen test is safe for the baby and helps to identify any chromosomal, some of the genetic defects or developing problems in the unborn baby such as Down's syndrome, problems in the spinal cord, brain or other neural tissues of the central nervous system etc.
There is a significance of each biomarker, identified by Quad Screen test. Each biomarker serves the purpose of identifying the abnormalities in the babies’ health. The higher AFP levels in the blood, identified during the Quad Screen test, help to identify neural problems like spina bifida. However, if the AFP levels are low, then the woman is at the risk of bearing the baby with Down’s syndrome. The high levels of hCG and inhibin A also indicate the risk of Down’s syndrome. If unconjugated estriol levels are low, the woman is again at risk of Down's syndrome.
The test provides certainty of a healthy pregnancy if the risk level is low. Approximately, 1 in 720 babies has Down’s syndrome at the time of birth. A Quad test can diagnose 85-90% of the cases of Down’s syndrome in the women aged 35 or above and hence is a very effective test and is critical for the expecting mothers to undertake.