SCREENING, TESTING and Down’s Syndrome INTRODUCTION Screening is an extremely their pregnancy. Many accept emotional issue. Expectant screening as routine, something parents therefore need to have that will reassure them that clear information about each all is well. stage of the screening process There has always been and what the possible outcomes recognition that the risk of having may be. Screening should be seen a baby with Down’s syndrome as a means of assisting parents to increases with maternal age. make informed choices about In the past, screening was only their pregnancy. offered to women over a certain Screening and testing for age. However, the majority of Down’s syndrome (and Spina children are born to women in Bifida) is now common practice. their twenties and early thirties, Many women enter into the and 75% of babies with Down’s screening process without much syndrome are born to women in explanation as to why they are this age group. In recent years, being screened and what the screening has increased to include possible implications may be for women of all ages. 1 MATERNAL SERUM SCREENING Maternal Serum Screening e.g. 1 in 300, or as a positive or (MSS) is offered to all women at negative screening. Having a about 15-16 weeks into pregnancy. positive screening (increased risk) A blood sample is taken from the does not mean that the baby will mother’s arm. The blood test is definitely have Down’s syndrome. called the double test or triple test Having a negative screening (low depending on which hormones are risk) is not a guarantee that the used as part of the test. It is baby will not have Down’s sometimes called the Bart’s test. syndrome. The sample is sent to the lab and A risk value of 1 in 300 is an tested for certain hormones and indication of the chance that the proteins. These are AFP (alpha baby will have Down’s syndrome. fetoprotein) and hCG (human It means that 299 people with this gonadotrophin) with or without risk will not have a child with Oestriol. The test measures the Down’s syndrome and only one levels of the proteins as a person will. percentage. This is used in The sensitivity rates for serum conjunction with the mother’s screening vary. 40% of Down’s age, weight and exact gestation, syndrome pregnancies will not be to assess the chance, or risk, of detected. For every one that is the baby having Down’s syndrome. identified, 60 unaffected The results of the test are pregnancies will be given anxiety expressed as either a risk value, provoking false positive results. 2 ULTRASOUND SCAN The ultrasound scan is part of woman further screening. This is the screening process. Scans are generally based on a risk value of usually performed at around 1 in 250 because this figure is 12 weeks and again at 18 weeks. close to the spontaneous The scan is not simply a chance miscarriage rate caused by for parents to have a look at their amniocentesis. Most parents baby. The radiographer will use would not consider the risk of the scan to look for thickening or miscarriage worthwhile if it is swelling at the back of the neck. significantly greater than the This is called nuchaltranslucency. chance of Down’s syndrome The scan will also look for being diagnosed. shortened length of long bones Parents who have been told that and a sandal gap between the first there is a high risk of their baby and second toe. Ultrasound having Down’s syndrome need to cannot diagnose Down’s have time to gather their syndrome, or exclude it. However, thoughts and decide on what if the above markers are seen, steps to take. Some parents will the possibility of the baby having decide against any further testing. Down’s syndrome is increased. Others will feel that they need to Many hospitals have an automatic know for definite, whether or not cut off point from offering a their baby has Down’s syndrome. 3 AMNIOCENTESIS AND CHORIONIC VILLUS SAMPLING Amniocentesis and Chorionic Amniocentesis and there is Villus Sampling (CVS) are both currently some debate about invasive tests that can give a whether the procedure can lead definite diagnosis that the baby to other birth defects. CVS and has Down’s syndrome. Amniocentesis results can take up to three weeks, a time of great Amniocentesis involves a very fine anxiety for the parents. needle being passed into the womb, under guidance by the There is also a technique called FISH ultrasound. A sample of the (fluorescence in-situ hybridisation) amniotic fluid is taken from based on genetic engineering around the baby. This test is done methods. A slide of amniotic fluid under local anaesthetic and is analysed using chromosome carries a risk of miscarriage specific probes. Results can be believed to be between 1 – 4%. available in a few days. Women This means that for every baby still have to have an amniocentesis, that is diagnosed as having as this is the method by which the Down’s syndrome, up to 4 babies amniotic fluid is collected. who do not have Down’s Although Amniocentesis and syndrome are miscarried. CVS will tell parents for definite In Chorionic Villus Sampling, cells whether their child does or does are collected from around the not have Down’s syndrome, the placenta. CVS carries the same tests cannot identify all conditions, risk of spontaneous miscarriage as or guarantee a healthy baby. 4 WHAT HAPPENS NEXT? No one can tell parents what children with Down’s syndrome. to do or how to feel. The right Another choice is to have a decision for one family might be termination. very different for another. Some people feel that they need to Whilst each individual’s right to know for sure whether their baby make their own choice is has Down’s syndrome and choose respected, Down’s Syndrome to have further testing, while Scotland hope that parents will others decide to wait and see. gather as much information as possible before making their For those who find out that they decision. Down’s Syndrome are carrying a baby with Down’s Scotland do not endorse the syndrome, there are several termination of pregnancy simply options. Some families use this on the basis that the baby has, or time to prepare for the birth of may have, Down’s syndrome. their baby with Down’s syndrome. Down’s Syndrome Parents who would not consider Scotland can help with a termination of the pregnancy information at this stage. Some should Down’s syndrome be babies are adopted. There are detected, do not usually undergo always families willing to adopt the amniocentesis as they would 5 not want to risk losing the baby. There can be the feeling of In some instances, people have a urgency about making decisions definitive test so that they can during pregnancy. People are prepare themselves and their often expected to respond families for the birth of a baby quickly about how they want to with Down’s syndrome. These proceed. Expectant parents parents will have weighed up the should not feel that they are being possibility of losing the child rushed and should be given all the against the need to know for relevant information that is definite. available to help them. Time should be taken in making any Around 80% of women who have decisions. Another twenty-four an increased risk after Maternal hours may not change initial Serum Screening go on to have an thoughts, but it will allow time to amniocentesis. ensure that the decision is right for them. 10% of those who have a positive amniocentesis continue with their Counselling should be available pregnancy comfortable in the through the hospital. Down’s knowledge that their baby has Syndrome Scotland also offers Down’s syndrome. support and further information. 6 A REMINDER OF THE MEDICAL TERMS AND THEIR MEANINGS Screening – A blood sample or a Human chorionic scan which gives a risk factor of gonadotrophin – A hormone the baby having Down’s syndrome. produced by the placenta. Screening is not conclusive and Oestriol – One of the female sex only further testing can give a hormones produced by the ovaries. definite diagnosis. False positive – Results of Testing – A procedure that can maternal serum screening indicate give conclusive evidence of that the baby has Down’s Down’s syndrome. syndrome when in actual fact it Invasive – Procedures which does not. involve passing a needle into the False negative – Results of womb to collect a sample of the maternal serum screening indicate amniotic fluid. that the baby does not have Maternal Serum – The mother’s Down’s syndrome when actually blood. it does. Amniotic fluid – The fluid Sandal gap – The space between contained in the amniotic sac the big toe and the second toe is which surrounds the baby. wider than usual. Alpha fetoprotein – A protein Chromosomes – Threadlike produced by the baby that is structures in the cells that contain present in the amniotic fluid. the hereditary genes. For further information contact Down’s Syndrome Scotland 158-160 Balgreen Road, Edinburgh EH11 3AU Telephone: 0131 313 4225 Fax: 0131 313 4285 Email: [email protected] Website: www.dsscotland.org.uk Printed June 2002.