Nuchal Scanning (11-13 Weeks)

The vast majority of babies are normal. However all women, whatever their age, have a small risk of delivering a baby with a physical and/or mental handicap. In some cases the handicap is due to a chromosomal abnormality.

The most common chromosomal abnormality seen is Down's syndrome. The only way to know for sure whether or not the fetus has a chromosomal abnormality is by having an invasive test such as an amniocentesis or chorionic villus sampling (CVS). These test carry a risk of miscarriage of approximately 1%.

The Nuchal Scan is the single most accurate, non-invasive technique estimating the risk of the fetus having Down's syndrome. With non-invasive testing there is no risk of miscarriage. However the screening test only assess your risk and does not give a definitive answer. It is carried out at 11-13 weeks and depends and the amount of fluid behind the neck of the fetus.

It is now recommended that you do not have this test alone but add a blood test to make the result more accurate. This Combined test measures both the NT scan and the level of hormones in the mother’s blood to give a risk factor (all done under 13 weeks). Over all the detection rate is 85%. Using the Combined test, 4.2% of women will be advised to go on to have an amniocentesis to confirm or exclude a chromosomal abnormality.

Irrespective of whether or not you decide to have an invasive test once you have the screening test result, it is recommended that you have a scan at 20 weeks to check for different physical abnormalities.