Screening Tests

Down Syndrome

Down syndrome is a chromosomal abnormality, in which there is an extra ‘chromosome number 21’ in the individual. This condition is characterized by certain features such as

Down syndrome is known to occur in 1 in 800 pregnancies. A pregnant woman of any age can have a baby with Down’s syndrome, though the chance increases with the mother’s age. 

Therefore, all pregnant women are offered a screening test to evaluate the ‘chances’ of their baby having this condition. The available screening tests include:

  1. Combined test (Combines USG scan and blood test)
    1. Performed between 11 and 14 weeks.
    2. An USG is performed to measure Nuchal translucency (Fluid thickness behind the baby’s neck) and assess nasal bone status. Then, a blood sample is drawn from the mother to measure the levels of two hormones (free beta-HCG and PAPP-A). 
    3. Then, using the mother’s age along with the above four parameters, the probability for Down’s syndrome is calculated.
  2. Quadruple test
    1. Patients who have missed the window for the ‘Combined test’ are offered Quadruple test, which is performed between 15 to 20 weeks. 
    2. Blood is drawn from the expectant mother and levels of specific hormones such as Alpha Fetoprotein, free beta-HCG, Unconjugated Estriol and Inhibin A are measured to calculate the chance.
    3. The pick-up rate of the quadruple screening test is lower than that of the Combined test; 80% Vs 90%. In both tests, false alarms are common and occur in 5% of women. 
  3. Non-Invasive Prenatal Test (NIPT)
    1. This is a relatively new test and involves evaluating cell-free DNA of the baby in the mother’s blood sample. 
    2. NIPT is a highly accurate screening test (pick-up rate is 99%, false alarm is less than 1%) and can be done starting from 10 weeks of pregnancy. The test, however, may not yield a result in around 4% of patients. 

For most women, a screening test returns a ‘lower-chance’ report and they are reassured. But in a few (5%), the test returns a ‘higher-chance’ result, in which case they are offered an appointment to discuss the option of undergoing a confirmatory test (CVS or Amniocentesis).

Pre-Eclampsia

Pre-Eclampsia (PE) is a condition characterized by development of high blood pressure and dysfunction of multiple organs. It affects about 5-10% of pregnant women and typically manifests after 20 weeks of pregnancy. Pre-eclampsia, when severe, can be life threatening to the mother and baby. Currently, the only treatment available for PE is monitoring and timely delivery.

Fortunately, research has shown that Aspirin can reduce the chances of developing early PE (defined as PE necessitating delivery before 32 weeks) by 90% and pre-term pre-eclampsia (defined as PE necessitating delivery before 37 weeks) by 60%. 

It is therefore recommended that all pregnant women at high-risk for early / preterm PE, be administered Aspirin, starting from <16 weeks and continuing till 36 weeks of pregnancy. 

A relatively simple screening test is available that can identify women at high-risk of PE. The test is performed in the first trimester between 11 to 14 weeks and utilizes the following information: