Screening for Down Syndrome and Other Chromosomal Abnormalities

One of the important decisions in your first trimester is whether or not to have screening for common chromosomal abnormalities like Down Syndrome, Edward Syndrome or Patau Syndrome. These conditions can cause learning difficulties, cardiac and other structural defects and can have other implications for the baby including the risk of miscarriage, stillbirth and lifelong health problems.

There are two main screening tests for these conditions in the first trimester (1) the Combined Test and (2) Non Invasive Prenatal Testing (NIPT).

Combined Test

Most UK hospitals offer a Combined Test (a scan and blood test at 11 to 13 weeks). Factors such as maternal age, the amount of fluid underneath the skin at the back of the baby’s neck (nuchal translucency) and two hormones (B-hCG and PAPP-A) are used to calculate the risk of the baby having one of these conditions. If the risk is more than 1:150 then a follow on diagnostic test such as Chorionic Villus Sampling (CVS from 11-14 weeks) or Amniocentesis (after 15 weeks) would be offered.

Both tests are invasive and carry a small risk of miscarriage. The Combined Test can detect about 5 out every 6 babies (85%) with Down Syndrome but 1 in 40 women (2.5%) having the test would be flagged up as high risk even if the baby was normal and if they had an invasive test would run the risk of miscarriage.

Non Invasive Prenatal Testing (NIPT)

Non Invasive Prenatal Tests (NIPT), like the ‘NIFTY’ Test, involve taking a simple blood sample at any time from 10 weeks of pregnancy. It can detect 99 out 100 babies with Down Syndrome, Edward Syndrome, Patau Syndrome and also some other rarer conditions; it can also detect the gender of the baby. It works by extracting some of the baby’s DNA from the mother’s blood stream. Only 1 in 1000 women (0.1%) having the test would be flagged up as high risk if the baby was normal and so very few would lead to a CVS or amniocentesis and the associated risk of miscarriage. Currently NIPT is the most accurate and safe screening test for many of these common chromosomal abnormalities.

We recommend the NIPT blood test to any pregnant women who wants an early, accurate (over 99% detection rate), safe screening test for these common chromosomal abnormalities. We use the NIFTY Test from BGI because it is the most validated NIPT Test at present, with over a million tests performed to date, and because it will also identify many of the other less common chromosomal abnormalities. The reporting of baby’s gender is, of course, optional.