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Quad Screen Test

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.

Why it’s done? What are the risks? How to prepare for the procedure? Expected results from the test: FAQ Section:

Quad screen is performed to identify the birth disorders and the risks of continuing pregnancy.

Depending upon the timing of pregnancy and other symptoms experienced, the women might be advised to go for other prenatal tests in addition to the Quad screen by the doctor. Some of the other tests, which might be recommended along with Quad Screen test, include the first-trimester screening which includes an ultrasound and a blood test. The women who are about to undergo the quad test should thoroughly consider all the factors and then go for the test.

The quad test is completely safe and is extremely helpful for the families in understanding the overall health of the unborn and in understanding if the baby would be born with some genetic and birth defects. Quad screen test is a routine screening prenatal test wherein a blood sample is taken from the mother to assess the health and well-being of the baby. Since this test involves a simple blood test.

It is a simple blood test so there are no specific steps to be followed. The woman can eat and drink normally. The blood sample is withdrawn from the arm of the pregnant woman and sent to the lab. It takes only 5 to 10 minutes to take the sample.

The blood sample taken from the patient would be taken to the lab and the department would prepare the report from the test. The report, once prepared would be handed over to the doctor and the doctor would discuss the report in detail with the patient and the family. The report of the patient, might show normal or abnormal results as mentioned below.

Normal Results: The normal levels of AFP, UE, hCG, and inhibin-A provides indication that the woman and the baby are in a healthy state. In such case, the doctor might ask the mother to take regular precautions and undergo other tests, if there is some confusion in the results.

Quad screen test can predict birth without major complications and healthy baby in over 98% of the pregnancies.

Abnormal Results: A positive or abnormal Quad test is attributed to the following reasons:

  • Not calculating the correct time or the week of pregnancy
  • In vitro fertilization
  • Numerous pregnancies
  • Diabetic condition
  • Smoking during the pregnancy

If the result is positive, the woman is advised to go for an ultrasound test, which will further confirm the number of babies and the gestational age. During the ultrasound the healthcare provider can also point out if the baby has any growth issues, if the placenta location is correct or if the baby is suffering from any chromosomal defects e.g. Down’s syndrome. In approximately 5 % of the women, undertaking the test, the result comes out to be false-positive, which means that the result is positive however, the baby actually does not have any disorder.

There can be certain cases of false-negative as well which means that if the test results from the Quad screen test indicate that the risk of carrying the baby by the mother is low, the probability of having any disorder in the baby at the time of birth cannot be completely ruled out.

In case, the test results are positive, the patient is recommended to go for some additional tests to get a clear diagnosis of the defect in the child. Some of the tests, which can be undertaken, in such scenario, as mentioned below.

  • Amniocentesis – The test examines the amniotic fluid around the baby and the AFP levels.
  • Targeted ultrasound – A patient is usually advised, by the doctor, to go for an Ultrasound if the Quad test comes positive. The Ultrasound, however, is not very effective in detecting Down’s syndrome. In order to detect the possibility of Down’s Syndrome, the patient is asked to go for Ultrasound along with amniocentesis. However, USG cannot pick up all cases of Down syndrome.
  • Noninvasive prenatal testing – The test analyses the circulating fetal DNA in the woman’s blood. This assists in identifying the risk of continuing pregnancy if the unborn has Down’s syndrome or any other chromosomal disorders. The pickup rate for the testing is 99%.
  • Chorionic villus Sampling - Chorionic villus Sampling should be considered if the woman is at a high risk of any genetic or chromosomal defect. The test is done between 10- 12 weeks of pregnancy. In this test, a small tissue sample is extracted from the placenta for further testing. CVS possesses a slight risk of miscarriage and is not that helpful in detecting neural issues like Spina Bifida.

Q1. Are there any other reasons for the high levels of the four substances- hCG, AFP, Inhibin A and UE in the blood, in case of the positive result?

A1. There can be multiple reasons for high levels of AFP in the blood. Some of the key reasons are listed below.

  • Death of the unborn baby inside the mother’s womb
  • If any part of the skull or brain is missing. (Anencephaly)
  • Intestines or any surrounding organs are defective (Duodenal atresia)
  • A heart defect – Tetralogy of Fallot
  • Spine defect – Spina Bifida
  • Genetic Defect– Turner’s syndrome
  • A woman carrying more than one baby

Reasons for high levels of inhibin A and hCG and low levels of estriol and AFP might be due to:

  • Edwards syndrome (trisomy 18)
  • Down’s syndrome (trisomy 21)

Q2. Are there any other names for this Quad screen test?

A2. Some alternative names for the Quad Screen test are:

Birth defect – quadruple, uE3 – quadruple, Unconjugated estriol – quadruple, Pregnancy – quadruple, AFP plus, AFP maternal, Triple screen test, 4-marker screen, Trisomy 21 – quadruple, Down syndrome – quadruple, Turner syndrome – quadruple, Tetralogy – quadruple, Spina bifida – quadruple, Duodenal atresia – quadruple.





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