The most common tests offered are ultrasound, nuchal, chorionic villus sampling, and amniocentesis. Here we explain and help you to understand the pregnancy tests:
| Test | Method | Screening or diagnostic | When it can be done |
| Ultrasound | Scan | Screening and diagnostic | From about 4 weeks |
| Combined test Nuchal translucency test and blood test |
Scan and blood test | Screening | Around 11-13 weeks + 6 days of pregnancy |
| Chorionic villus sampling |
Analysis of placental tissue | Diagnostic | Around 11- 13 weeks |
| Amniocentisis | Sample of amniotic fluid is tested | Diagnostic | 13 + weeks |
| Triple Quadruple | Blood tests | Screening | 15 -20 weeks |
Before you can make any decisions about which antenatal tests to have (or whether to have any at all), the first thing to understand is the difference between a screening test and a diagnostic test.
- Screening test – tells you what your risk is of having a baby with a particular health problem.
- Diagnostic test - tells you whether your baby has or has not got a particular health problem.
Screening tests
A screening test estimates your risk of having a baby with a serious health problem such as Down’s syndrome or spina bifida or some rarer condition such as Edward’s syndrome, Patau’s syndrome. It can’t tell you for certain whether your baby has or has not got one of these conditions.
So, for example, you might have a blood test when you are 16 weeks pregnant and be told that your risk of Down’s syndrome is 1 in 140. This means that there is a one in 140 chance that your baby will have Down’s syndrome. Or, to look at it another way, you are far more likely to have a normal, healthy baby than a baby with Down’s syndrome.
| Name of screening test | When you can have the test |
| Nuchal translucency test | 11 – 13 weeks + 6 days of pregnancy |
| Ultrasound scan (although this may be diagnostic in some cases) | |
| Blood tests | 11 – 20 weeks of pregnancy |
Screen negative
The result of your screening test may simply be described as screen negative. This means that your risk of having a baby with a problem is less than 1 in 250. Your risk is so small that it’s not even quantified. Nonetheless, a screen negative result does not mean that you definitely have a healthy baby.
Screen positive
If your test result is screen positive (ie, greater than 1 in 250) you will be quoted a figure such as 1 in 100 or 1 in 40. Only you can decide whether you are prepared to accept that risk or whether you want to have a diagnostic test to get more information - there’s more about making these difficult decisions later on.
Diagnostic tests
A diagnostic test can tell you whether your baby has Down’s syndrome or spina bifida or other major health problems. The result gives you a yes or no answer.
Name of diagnostic test
| When you can have the test | |
| Chorionic villus sampling |
Around 11- 13 weeks of pregnancy |
| Amniocentesis | 13 + weeks of pregnancy |
| Ultrasound scan (although this may only be a screening test in some cases) |
Any time from 4 weeks of pregnancy |
