Screening and diagnostic tests

Screening tests assess your risk of having a baby with a chromosomal abnormality such as Down syndrome or a neural tube defect such as spina bifida, but they don’t provide a definite diagnosis.

Because screening tests aren’t invasive, and carry no risk of miscarriage, they’re normally the first step that pregnant women take.

Screening tests include ultrasound scans, such as the nuchal translucency scan which is performed as part of your first trimester screen at around 11-13 weeks and checks for signs of Down syndrome; and blood tests, carried out at 15-20 weeks to check for neural tube defects. These tests will tell you your statistical risk of having a baby with a particular problem. If you’re ‘screen negative’ this means that the risk of having a baby with this problem is low enough not to be considered a problem; if you’re ‘screen positive’, you’re considered to be at a high enough risk to have a diagnostic test.

It’s important to recognize that being ‘screen positive’ doesn’t mean your baby is definitely affected by this condition. Many of the women who get positive results go on to have perfectly healthy babies. These cases are referred to as false positives.

Diagnostic tests are able to tell you for sure whether your baby has a certain condition. They include certain types of ultrasound scans, CVS (chorionic villus sampling) and amniocentisis and chorionic villus sampling. These tests are invasive and carry a small risk of miscarriage that, for some women, outweighs the benefit of being tested.

The information in this feature is intended for educational purposes only. If you have any concerns about your health, the health of your child or the health of someone you know, please consult with a doctor or other healthcare professional.