What is Screening?
Screening is a way of identifying an increased chance of your unborn baby having a particular genetic condition. All woman are now given the option to screen in the first trimester of pregnancy. Screening is always optional and is a women’s choice. The program in the UK currently offers screening for many conditions. This page will help you to understand the screening process for: Down’s Syndrome, Edward's Syndrome and Patau’s Syndrome.
How does it work?
First you will be offered a combined screening test. This will inform you of the likelihood of whether your baby may have Down's Syndrome, Edward’s Syndrome or Patau’s Syndrome. This information is gathered by using a combination of a maternal blood test, maternal age, and a measurement taken from the back of the neck of the fetus on ultrasound between 11 and 14 weeks.
This test will not be able to give you a definitive 'yes or no' answer about whether your baby will have one of these anomalies. Instead, the results are provided as a list of 'chances'. If the 'chance' of one of these conditions is more likely than 1 in 150, then further tests will be offered to you.
At this point you can choose if you would like to have further testing. If you are unsure what to do at this stage, you will be able to talk through the decision and the options with your screening midwife.
You may have diagnostic testing. This is offered in the form of chorionic villus sampling (CVS), which can be performed between 11 and 14 weeks of pregnancy; CVS involves taking a needle sample of placental tissue.
Alternatively you may have an amniocentesis from 15 weeks of pregnancy onwards. Amniocentesis is performed using a needle to take a sample of the fluid that surrounds the fetus. Samples are sent for tests that identify certain inherited conditions, but not all.
Both CVS and amniocentesis testing carry a small chance of spontaneous miscarriage.
You may also be offered a NIPT (non-invasive prenatal test). This is a recently developed blood test that is on offer in some hospitals. I t works by examining fragments of DNA detected in the mother's blood. The majority of these fragments of DNA will be the mothers but a few will be from the placenta of the fetus. From there it is possible to detect the amount of chromosomes present in the DNA and specifically if trisomies consistent with Down's Syndrome, Edward's and Patau's Syndrome are present.
The NIPT test can be carried out from 10 weeks of pregnancy, but most women will have the combined screening text first.