Types of prenatal tests
We distinguish between:
- Screening tests that are used for risk calculation (What is your baby’s chance of having an abnormality?)
- Diagnostic tests that are administered to verify the accuracy of the diagnosis These tests are more invasive, so they entail greater risk.
How great is the risk that my child has Down syndrome?
All women at any age are at risk of giving birth to a child with a chromosomal defect, such as Down syndrome (trisomy 21). As the mother's age increases, so does the risk of chromosomal abnormalities in her baby.
Down syndrome occurs in about 1 in every 700 babies. At age 35, a woman’s risk of having a baby with Down syndrome is 1 in 270 at age 40, this risk increases to 1 in 80.
What are the testing options?
There are two screening tests to calculate the risk of chromosomal abnormalities in your baby: the non-invasive prenatal test (NIPT) and the nuchal translucency measurement (NTM).
What if the test indicates a higher risk of a chromosomal abnormality?
After the NIPT or NTM is performed and the risks are calculated, it is up to you and your partner to decide whether the risk of a chromosomal abnormality is high enough to proceed with invasive testing: chorionic villus sampling or amniocentesis.
If there is an increased risk of an open neural tube defect, a detailed ultrasound scan will be sufficient to confirm the diagnosis.
Chromosome abnormalities: certainty through chorionic villus sampling or amniocentesis
The only way to know with certainty that your baby does not have any major chromosomal abnormalities is to perform chorionic villus sampling (CVS) after 11 weeks of pregnancy or an amniocentesis after 15 weeks.
These two tests, however, are not without risk: the risk of a miscarriage following chorionic villus sampling and amniocentesis is approximately 0.3%.
Indications for invasive tests
The procedures for chorionic villus sampling or amniocentesis are applied more frequently when the risk of a chromosomal abnormality is high.
Invasive testing is often opted for in the following cases:
- A family history of hereditary or congenital disorders
- A previous child with a hereditary or congenital disorder
- You are over the age of 35
Whether or not you choose to have an invasive test done, we recommend having an ultrasound scan around 20 weeks in case of any increased risk. For foetuses with increased neck thickness (≥3 mm), an additional ultrasound scan is recommended around the 15 to 16 week mark, as the babies run an increased risk of heart defects and other abnormalities.
- Think carefully before having a prenatal test performed. Consider beforehand what you will do if the results are not very good.
- We are aware that this issue can raise many questions, and are always willing to help guide your decision. Do not hesitate to ask us for help.
- Some women do not want to know if their baby has any abnormalities or what the thickness of the nuchal fold is. In these cases, we will respect the mother’s wishes. However, you must notify us about your wishes before a test is administered.
- Once you are thoroughly informed and have made your decision, fill in the form you received during the consultation.