Screening tests available during pregnancy


Nuchal Fold Scan

The nuchal translucency test, or nuchal fold scan, was introduced in 1995 and allows 'risk assessment' of foetal chromosomal abnormalities such as Down syndrome. Via an ultrasound scan it measures the fluid accumulation (or nuchal translucency) in the neck of the developing foetus. To be accurate it must be carried out between 10-14 weeks into pregnancy, meaning that any problems will be spotted early on. Nuchal fold scans have a roughly 80% detection rate for Down syndrome.

Studies carried out in March 1998 and published by the University of California, show that in addition to detecting chromosomal abnormalities the nuchal fold test has the potential to be used for diagnosis of other foetal problems and genetic disorders. This test originated at the Harris Birthright Research Centre and has been applied to over 100,000 pregnancies in Europe already. It is available in 48 countries in more than 1,000 units and in Australia is routinely offered to pregnant women.

The test is now reasonably widely available in the UK and you may be offered it routinely if you are 35 or over. Participating hospitals have to have the right ultrasound equipment, plus a special certificate issued by Professor Kypros Nicolaides, Director of the Harris Birthright Research Centre and access to the database is needed to accurately assess the risk of foetal abnormality.

Professor Nicolaides believes that the nuchal fold scan is also of particular importance in twin pregnancies, as at this early stage of pregnancy - and only then - ultrasound can be accurate in assessing the membrane structures. This means that the scan can pinpoint whether twins are sharing a chorionic membrane (the sac in which the baby lies), or not. Knowledge of this fact helps to plan the way in which the pregnancy will be managed. Where the twins are sharing the same chorionic membrane rather than having one each, the risk of complications is much higher. There is a six times greater risk of miscarriage, double the risk of a pre-term birth and perinatal death and four times the risk of severe retarded growth affecting one or both twin. It is therefore vital to try and get this test if at all possible.

If the test isn't available in your area and you want one, your GP can refer you to the Fetal Medicine Centre (www.fetalmedicine.com) direct for an immediate test, but since the centre is privately run you will have to pay for it. The current cost is around 100+. Alternatively, you can telephone the centre every day at 10am - 020 7034 3070 - to see if there are any appointment cancellations. As at the time of writing, around 90 centres in the UK offer private tests.

For a list of registered centres throughout the world that perform a nuchal fold scan click here.

Latest research

Scientists at King's College Hospital and St. Bartholomew's Hospital and the Antenatal Screening Service at the Wolfson Institute are researching the viability of an "integrated" test for Down syndrome. This would encompass the nuchal fold scan, PAPP blood tests in the first trimester and then a quadruple blood test carried out in the second trimester. Combined with the mother's age, the results can be analysed to assess the risk of Down syndrome. The researchers are predicting a high detection rate - 90%, and a low false-positive rate - 1-2%. However, because the second blood test would not be carried out until the second trimester of pregnancy, results could be delayed until as late as 22 weeks into the pregnancy. On the plus side, they could be given as early as 14 weeks into pregnancy.

The Dr Foster Good Birth Guide provides information on how maternity care is delivered in the UK and gives details of the services offered by individual maternity units. It has been designed to help you find the maternity care best suited to your individual needs.

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'Double', 'Triple' and 'Quadruple' Test

These are 'screening tests' that measure the level of hormones in the blood and provide an 'estimation of risk' for chromosomal abnormalities such as Down syndrome and Trisomy 18 and ventral wall defects (abdominal wall defect). Most women have the 'Double' or 'Triple' test which measures two or three 'markers', but some have a 'Quadruple' test (the more markers used, the more accurate the test). The tests are available to anyone free of charge at around 16-18 weeks of pregnancy, although only 70-80% of women are offered blood screening tests, despite the fact that they are easy and cheap to carry out.

These tests can also help to identify women who may be carrying twins, or women who may be farther along or not as far along in their pregnancy as was thought. Abnormal test results have been associated with premature delivery, low birth weight babies, abnormal placental findings and miscarriage. 65% of Down syndrome cases and 85% of neural tube defects are detected by these tests.

If a result indicates your are at 'high risk', you may be offered an amniocentesis or ultrasound in order to provide more information about your pregnancy. However, it is worth noting that many factors can influence the result of the tests e.g. if the mother is overweight, or there has been recent vaginal bleeding it can cause abnormal hormone levels.

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Diagnostic Tests

Read about the various diagnostic tests available during pregnancy.

USEFUL RESOURCES:

NHS Direct - 24-hour nurse-led helpline with confidential healthcare advice and information
List of NHS Trusts
NetDoctor.co.uk - information on children's health & diseases
The Fetal Medicine Foundation
Harris Birthright Research Centre (originators of nuchal fold scan)
Medical Dictionary