Tests at 10-13 weeks
• Chorionic Villus Sampling (CVS) is the only diagnostic test widely available to women before 14 weeks of pregnancy. There is a 0.5 to 2% risk of miscarriage following the procedure, which is an important factor to take into account. Ask your hospital what its percentage regarding testing and miscarriage is, and how many tests it carries out.
CVS involves taking a tiny sample of the placenta by inserting a fine needle through the wall of the abdomen or via the cervix. Ultrasound scanning helps the sonographer position the needle correctly. The sample is sent away to a laboratory and you should receive the results within 7 to 10 days.
• A Nuchal Translucency Scan is a screening test that is not available everywhere, so you may need to have it done privately. A thin layer of fluid between two folds of skin at the back of your baby's neck is measured. Research suggests that the test is good at predicting which women have the highest risk of being pregnant with a baby with Down's syndrome, although it is more accurate for women over 35 years of age.
• Blood tests
If your blood test shows that your risk of being pregnant with a baby with Down's syndrome is less than 1 in 250, your result will be described as screen negative.
This does not mean that you definitely aren't pregnant with a baby who has Down's syndrome, it only means that it's very unlikely.
If your blood test shows that your risk is more than 1 in 250, your result will be described as screen positive.
This means that your risk of a Down's baby is higher and you may want to have a diagnostic test, such as an amniocentesis, to find out.
• Amniocentesis test
Amniocentesis is normally carried out at about 20 weeks, although a few hospitals offer it much earlier (before 14 weeks). Like CVS, the procedure involves using ultrasound scanning to guide a long needle through the wall of your abdomen into the womb from where about 20mls of amniotic fluid is withdrawn. It's not usually painful.
There is a 1-2% risk of miscarriage following amniocentesis and you will be advised to rest for a couple of days. The results take anything from a week to three weeks to come through.
See Your pregnancy - 14-28 weeks/ultrasound scan