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Diagnostic tests can tell you for certain if your baby has a chromosomal abnormality such as Down's syndrome, or a structural defect such as spina bifida (screening tests cannot do this on their own). Some diagnostic tests, amniocentesis and CVS for instance, are invasive procedures that carry a risk of miscarriage of around 1%. AmniocentesisThis test is usually done around the 16th week of pregnancy. A needle is passed through the mother’s abdomen into the uterus, under ultrasound guidance, and a sample of amniotic fluid surrounding the baby is withdrawn. The fluid contains substances from the baby which can be tested for certain conditions such as neural tube defects - spina bifida and anencephaly - and cells which can be grown in culture. The cells can be tested for Down’s syndrome and other chromosomal and inherited disorders. Results will take about a week if the tests are on the fluid and up to 4 weeks if the cells need to be grown for chromosome analysis. For every 100-200 women who have this test at about 16 weeks it is likely that one will miscarry as a direct consequence of the test. Amnio Q-PCR and Amnio + F.I.S.H.Following the normal procedure for amniocentesis, fluid is taken from the amniotic sac surrounding the baby under ultrasound guidance. The fluid contains cells from the baby. Amnio-PCR and Amnio + F.I.S.H. are molecular tests which provide a rapid diagnosis of the three most common chromosome abnormalities including Down’s syndrome. Results take on average 2 to 7 days. At the moment only a few hospitals offer this to women. However many hospitals do have access to the facilities for performing these tests and often the tests can be paid for on a private basis. Chorionic Villus TestThis test, which is usually known as CVS (CV sampling) or CVB (CV biopsy), is a prenatal test which can be performed early in pregnancy, from 11 weeks. A sample of tissue that will form the placenta is taken either through the cervix or through the abdomen. The range of conditions that can be detected is similar to those for amniocentesis except that neural tube defects cannot be diagnosed. For every 100 women who have this test from the 11th week in pregnancy one will miscarry. Ultrasound ScanningThis is a technique used routinely in most hospitals to monitor the growth and development of the baby before birth. Scans before 16 weeks are useful for dating the pregnancy (and are able to detect some major malformations), detailed scanning at 18-21 weeks should show up any major malformations as well as some minor ones. | |
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