WebMD Oct 14 2016
Edwards’ syndrome diagnosis and screening
Most diagnoses are made in the antenatal period.
Pregnant women are offered screening for Edwards' syndrome between 10 and 14 weeks. This is known as the combined test and involves a blood test plus a nuchal translucency ultrasound scan.
Later they are offered a mid-pregnancy (18-21 weeks) ultrasound scan that looks for physical abnormalities and rare conditions, including Edwards' syndrome.
If these tests show the chance of your baby having Edwards' syndrome is higher than 1 in 150 you will be offered more tests, either amniocentesis or chorionic villus sampling. These are invasive tests and carry a small risk of miscarriage. Fluid or tissue is removed from the amniotic sac or placenta, which can then be tested to see if there is an extra copy of chromosome 18.
There is a privately available test which can be carried out from 10 weeks ofpregnancy. It involves taking a blood sample from the mother and testing the baby's DNA found within it. This is known as 'non-invasive prenatal diagnosis' NIPT. Its use is being evaluated by the NHS.