Prenatal Testing: What Are Your Options?

Prenatal testing plays a key role in monitoring the health of both the mother and the baby throughout pregnancy, ensuring that any potential complications are identified early on.

This article explains the different types of prenatal tests, when they are performed, and what happens if a prenatal test reveals an abnormal result.

What are the different types of prenatal tests?

Prenatal tests are divided into two main categories: screening tests and diagnostic tests.

Screening tests

Screening tests are non-invasive tests that assess the likelihood or risk of a condition. These tests don’t provide a definitive diagnosis but help your doctor identify pregnancies that might be at higher risk for certain conditions.

Common screening tests include:

First trimester screening: This screening is performed between weeks 11 and 14 of pregnancy. It combines a blood test (which measures hormone levels) and an ultrasound (which measures the fluid at the back of the baby’s neck) to assess the risk of conditions like Down’s syndrome and trisomy 18.
Second trimester screening: This screening is performed between weeks 15 and 20 of pregnancy. It involves a blood test that measures 4 substances in the mother’s blood to assess the likelihood of certain birth defects, including Down’s syndrome, neural tube defects, and trisomy 18.
Non-invasive prenatal testing: This test can be performed as early as 10 weeks of pregnancy. It involves a blood test that analyses small fragments of foetal DNA in the mother’s bloodstream to screen for conditions like Down’s syndrome, trisomy 13, and trisomy 18.

Diagnostic tests

Diagnostic tests are more invasive but provide a definitive result. These tests are typically recommended if a screening test shows a high risk of a particular condition or if there are other concerns.

Common diagnostic tests include:

Chorionic villus sampling: This test is performed between weeks 10 and 13 of pregnancy. It involves taking a small sample of tissue from the placenta to test for conditions like Down’s syndrome, cystic fibrosis, and sickle cell anaemia.
Amniocentesis: This test is performed between weeks 15 and 20 of pregnancy. It involves taking a sample of the amniotic fluid that surrounds the baby. This fluid contains cells from the baby that can be analysed for conditions like Down’s syndrome, and infections.

When are prenatal tests performed?

Prenatal tests are performed at different stages of pregnancy, depending on their type and purpose. While some tests are routine, others are recommended based on factors such as the mother’s age, medical history, or the results of earlier screenings.

In certain cases, additional tests may be performed during the third trimester (later stages of pregnancy). These may include glucose tolerance tests to screen for gestational diabetes, and other tests to assess the risk of preterm labour or complications.

Prenatal testing isn’t mandatory; it’s up to each patient to decide. However, if your doctor recommends a specific test for medical reasons, it’s essential to discuss its benefits and risks in the context of your specific situation. Prenatal tests provide valuable information that can help identify potential issues early in the pregnancy, enabling timely interventions and better preparation for the baby’s arrival.

What happens if a prenatal test shows an abnormal result?

Receiving an unexpected result from a prenatal test can be worrying, but it doesn’t necessarily mean there is a problem with the pregnancy.

If the result of a screening test is unexpected, the next step is often to offer a diagnostic test to confirm the result. For example, if a first-trimester screening shows a higher risk for Down’s syndrome, a diagnostic test like amniocentesis may be recommended to provide a definitive diagnosis.

On the other hand, if the result of a diagnostic test is unexpected, it can confirm the presence of a genetic disorder or birth defect. In these cases, genetic counselling will be provided to help you understand the results.

Above all, it’s important to remember that prenatal testing is just one part of the pregnancy journey.