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A Decision Aid Testing in Pregnancy for Fetal Abnormalities Contents A Decision Aid Testing in pregnancy for fetal abnormalities Contents Why has prenatal testing been offered to me? 2 What fetal abnormalities are tested for in pregnancy? 3 Chromosomal abnormalities 3 About Down syndrome 4 About Edwards syndrome 4 About Patau syndrome 4 About sex chromosomal abnormalities 4 Physical abnormalities 5 What are the different types of prenatal testing? 6 Screening tests 6 Understanding screening results when they are in words 9 Understanding screening results when they are numbers 10 What happens after the screening test? 11 What if I get an “increased risk” result on any screening test? 11 Support available after screening tests 11 Diagnostic testing 12 Chorionic Villus Sampling (CVS) 12 Amniocentesis 13 What happens after a diagnostic test? 14 What if an abnormality is diagnosed from testing? 14 Women’s stories 15 Resources 16 Prenatal Diagnosis and Genetic Counselling Services 16 Web sites 16 Work Sheet 17 Summary of Tests Inside back cover The aim of this Decision Aid is to assist women in early pregnancy to make decisions regarding testing for fetal abnormalities like Down syndrome. Introduction This Decision Aid will be useful to you if: • you are interested in learning more about prenatal testing • you are undecided whether or not to have testing or • you are unsure about which test to have. The Decision Aid is designed to be flexible to meet your individual information needs. • The table inside the back cover gives you a brief summary of the tests available. • The booklet provides information on the conditions that can be tested, the benefits and risks of the tests, how to make sense of the results and the resources available. • The worksheet at the back of this booklet is designed to help you weigh up the options. 1 Why has prenatal testing been offered to me? • Prenatal testing is made available because • Some but not all fetal abnormalities can be of the small risk that all women have of having detected during pregnancy. a baby with a major problem. • No single test checks for everything. • While the majority of babies are born without • There are different types of tests available. any abnormality, 3–4% of pregnancies result They vary in how accurate they are, how safe in babies with abnormalities. they are, when they are performed and what information they give. No birth defects Birth defects • A woman may decide to have testing: 96–97% of all babies have 3–4% of all babies have no abnormality an abnormality • because she wants to know more about her pregnancy, • because she wants the option of terminating an affected pregnancy or • so she can prepare herself for a baby with an abnormality. • It is important to understand that ultrasound is a test for fetal abnormality. Figure 1: Background risk of birth defects • A woman may decide not to have any prenatal testing. • Information on prenatal testing for abnormalities in the developing fetus is provided to all Testing for fetal abnormality is not women in pregnancy. compulsory for anyone. 2 What fetal abnormalities are tested for in pregnancy? • It is not possible to test for all fetal abnormalities in pregnancy. • It is important to remember that the vast majority of babies born, regardless of a mother’s age, do not have any of these 0 4 abnormalities. 1in 50 1in 70 90 Chromosomal abnormalities 1in 25 5 1 0 6 1in 1 6 22 5 1in 0 300 355 9 44 1in 000 • For normal human development we need 500 77 545 660 1 1in 8 1 1in 1in 1in 1in 1in 1in 1in 1in 46 chromosomes (23 pairs). age of mother 1in 9 5 1 31 30 32 33 34 35 36 37 38 39 40 41 42 43 4 44 46 5- 1 • Any extra or missing chromosome, or any 20-29 change in the structure or arrangement of the Figure 2: Risk of having a baby born at term with Down syndrome by age of mother chromosomes in the developing embryo, may affect normal development. About Down syndrome (also called Trisomy 21) • The chromosomal abnormalities that are most • Down0.05 syndrome is the most common commonly tested for in pregnancy result from chromosomal abnormality (1 in every 400 an extra or missing chromosome in the pregnancies).0.04 It is caused by having an extra developing fetus. chromosome (chromosome 21) and results 0.03 • The risk of these conditions caused by in a number of characteristic physical, medical an extra chromosome (eg Down syndrome) and intellectual features. 0.02 increases with a woman’s age (Figure 2), but • Many pregnancies with this chromosomal pregnancies of younger women can also abnormality0.01 miscarry. be affected. • Most individuals with Down syndrome have a0.00 mild to moderate level of intelligence and can participate in school, work and social life but others can be severely intellectually disabled. Physical abnormalities involving the heart and digestive system occur more often with babies with Down syndrome than 3 in babies without chromosomal abnormalities. About Patau syndrome (also called Trisomy 13) It is not possible during the pregnancy to predict • Patau syndrome is less common than the level of disability. Edwards syndrome (1 in every 3400 pregnancies) • The risk of having a baby with Down and is caused by having an extra chromosome syndrome increases with a woman’s age (chromosome 13). but pregnancies of younger women can also • Pregnancies with this chromosomal abnormality be affected. usually miscarry and babies that are liveborn • There is no cure for Down syndrome but are not expected to live. with early intervention such as individualised • All babies with Patau syndrome have severe educational programs, the chances of the child developmental problems. achieving his or her potential is maximised. • The risk of having a pregnancy affected with For further information go to the Down Patau syndrome increases with a woman’s age syndrome Association of Victoria website: but pregnancies of younger women can also http://www.dsav.asn.au/ be affected. About Edward syndrome (also called Trisomy 18) About sex chromosomal abnormalities • Edwards syndrome is less common than Down • The chromosome count for typical syndrome (1 in every 1600 pregnancies) and development of a girl is 46XX and for is caused by having an extra chromosome a boy is 46XY. (chromosome 18). • Sex chromosomal abnormalities occur • Pregnancies with this chromosomal abnormality when there is a missing or an extra copy usually miscarry and babies that are liveborn of the X chromosome or an extra copy rarely survive for long. of the Y chromosome. • All babies with Edwards syndrome have • Normal development is affected in a variety significant developmental problems. of ways depending on the chromosomal abnormality. • The risk of having a pregnancy affected with Edwards syndrome increases with a • These abnormalities are not known to be woman’s age but pregnancies of younger associated with a woman’s age. women can also be affected. 4 Regardless of a woman’s age, the risk of the Public Health Association of Australia of having a pregnancy with a chromosomal and the Spina bifida Foundation of Victoria: abnormality decreases as the pregnancy http://www.phaa.net.au/policy/folate and develops. This is because many pregnancies http://www.sbfv.org.au affected with chromosomal abnormalities will • Cardiac abnormalities such as conditions miscarry naturally during pregnancy, without involving the development of the blood vessels any intervention. or the heart’s structure. • It is not possible to accurately predict which • Digestive system abnormalities where there pregnancies will miscarry. is a narrowing or missing parts of the system. Physical abnormalities • Renal abnormalities such as blockages or poor development of the kidneys. • Some, but not all, physical abnormalities can be detected during pregnancy. It is important to remember that the vast majority of babies born, regardless of • Many of the abnormalities that are detected a mother’s age, do not have any of these can be treated once the child is born. abnormalities. • Most physical abnormalities are not related to the mother’s age, but some can be related to chromosomal abnormalities or other syndromes. The most common physical abnormalities include: • Neural tube defects such as spina bifida. These occur early in pregnancy when the spine fails to form properly and the spinal cord and/ or brain can be affected. Taking folate before and during early pregnancy is known to reduce the occurrence of neural tube defects. For further information go to the websites 5 What are the different types of prenatal tests ? Screening tests The tests available to check for • All pregnant women should be given abnormalities in pregnancy fall into appropriate written information and offered two groups: screening tests and prenatal screening, regardless of their age. diagnostic tests. • Screening tests do not have any additional • Screening tests can be blood tests from risk of miscarriage. the pregnant woman and/or ultrasounds • All screening tests give a risk result not of the fetus. These tests are available to a diagnosis. The result can be in words or women of all ages. numbers or both. • Diagnostic tests are tests that examine • Screening tests will miss some pregnancies samples of the developing placenta or fluid with Down syndrome. Detection rates vary taken from around the baby. A skilled depending on the test and the age of obstetrician should do this by inserting the woman. a needle into the woman’s abdomen to take the sample, guided by ultrasound. These • Screening tests are more accurate in women tests are available to women who have who are older. been identified as being at “increased Combined First Trimester Screening risk” because of their age or the results The information from two screening tests are of screening tests.
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