Screening And Diagnostic Tests - Is There A Difference?
Being pregnant can be confusing in many ways. You have hundreds of doctors appointments, thousands of precautionary measures to take care of and millions of tests. As exaggerated as these numbers may be, the emotions we are forced to go through during this time can be overwhelming. Amidst this chaos, you may begin to wonder why are you taking so many tests and what these tests mean. You may hear your doctor saying words like screening test or diagnostic test, and more often than not, you go through it without fully understanding the meaning of these terms. That’s where we come in.
So, let’s break down these terms and find out what they exactly mean.
Screening tests help the doctor assess the risk of a birth defect in your child. They aren’t harmful nor do they accurately indicate any defect in the baby’s development. They are a mere assessment or screening of whether the baby is more likely to have a birth defect. This would be indicated as a positive result on the screening test or a negative result. However, it is important to understand that this by no means is a conclusive result and simply assesses the chances.
Some screening tests include:
a) First-trimester screening
This test uses blood samples and ultrasounds to evaluate the risks of birth abnormalities like down syndrome or an abnormal heartbeat.
b) Maternal blood screening
Maternal blood screening tests are another way to evaluate the risks of birth defects in the baby. A blood sample is taken to test four elements. These tests are also often called quad screening, triple screening or serum screening.
c) Cell-free fetal DNA testing
This is a type of testing that is non-invasive. A sample of your blood is taken to assess your baby’s DNA and genetic makeup. This test is usually monitored at around 10 weeks of pregnancy.
Diagnostic tests provide us with more conclusive results and hence, are also more invasive than screening tests. Most women prefer to opt for screening tests and according to the result, move on to a diagnostic test. These tests don’t detect all birth defects, but do detect most chromosomal abnormalities, inherited and genetic disorders more accurately. However, it is important to note that some of these diagnostic tests do carry a bare minimal risk of miscarriage. Having said that, it is also important to note that most of these tests need to be administered to avert a greater risk.
Some of these tests include:
a) Chorionic villus sampling (CVS)
Here, the doctor will take a sample of the placenta for testing. This is done either by the transvaginal or transabdominal method. This test is used to detect chromosomal abnormalities and certain other birth defects.
A small sample of the amniotic tissue will be taken to test for fetal infections and chromosomal defects. It is often performed at around 15-20 weeks of pregnancy.