Ante-natal screening

There are various tests available to identify whether an unborn baby has Down’s syndrome.  However all tests fall into one of two categories, either screening or diagnostic. Screening is non-invasive while all diagnostic tests are currently invasive. Researchers are now seeking non-invasive diagnostic tests using urine or blood.

SCREENING TESTS:
These offer a very low risk to both mother and baby but can only provide an estimate of the chance of a baby having the condition. If the test is positive, they can be followed-up with diagnostic tests which are more precise.

Maternal Serum Screening: A sample of maternal blood is tested for hormones, between weeks 15 and 18 of pregnancy. Results are given within a week

Ultrasound Scanning: Defects in heart, kidneys or digestive system are indicative of the syndrome and can be picked up by skilled operators. In addition the Nuchal Fold Scan, carried out around the 12th week of pregnancy, measures the amount of fluid present at the base of the head. This is used in conjunction with maternal age to calculate the likelihood of Down’s syndrome. It should be noted that reliability of the fold test is uncertain, unless carried out by an expert centre in fold measurement.

DIAGNOSTIC TESTS:
These aim to detect the presence of the extra chromosome in a baby’s cells and give an accurate diagnosis in almost all cases. They carry a risk of miscarriage, ranging from 1% to 3%. Samples of cells are taken from the amniotic fluid, the placenta,  or – more recently – the umbilical cord. These tests are carried out between weeks 10 and 18 of pregnancy.  Results can take up to four weeks.

The Down’s Syndrome Association provides non-directive support and information for pregnant women undergoing, or considering undergoing, pre-natal testing for Down’s Syndrome.  The Association also campaigns to ensure that women who refusing screening, or who receive a positive result and decide to continue with the pregnancy, should be treated with dignity and respect.