5 June 2003

Best antenatal screening: study results

A study of about 50,000 pregnant women has shown that the integrated test for Down's syndrome offers a "significantly higher" level of safety than the screening available to most women in the UK. The study, which will be reported in the June Journal of Medical Screening, was carried out by Professor Nicholas Wald and colleagues at the Wolfson Institute of Preventive Medicine and University College Hospital. Their report also shows that the integrated test is best in terms of efficacy and cost.

Screening for Down's syndrome: what's available now
Without screening, 1 in 700 babies would be born with Down's syndrome. Some hospitals in the UK offer a method of antenatal screening at 16 weeks called the triple test, developed by Professor Wald and colleagues in 1988. This test detects two thirds of affected pregnancies, but it also identifies one in 20 pregnancies as being at risk of Down's syndrome when they are, in fact unaffected - a 'false-positive rate' of 5%. Most hospitals offer an even less sophisticated version called the 'double test'. The only way to be certain if the fetus has Down's is to perform a diagnostic test such as amniocentesis, an invasive procedure which has a 1% risk of miscarriage.

What is the integrated test?
The integrated test uses data gathered on two different occasions in pregnancy. At 12 weeks the mother has a blood sample test and an ultrasound test, and between 15-22 weeks she has the triple test, or ideally the newer quadruple test, which includes an extra marker. Only then does the medical team assess the risk of the baby having Down's syndrome, by analysing all the information.

What it means for patients
The integrated test improves safety (reduces the cost of miscarriage) by four-fifths. It detects half the cases the other tests miss. If screening is set to detect 85% of Down's syndrome cases, the existing quadruple test's false-positive rate means that 45 women in 100,000 would lose a healthy baby as a result of having amniocentesis. With the integrated test this figure is just 9 per 100,000.

What it costs
Although the integrated test is more expensive, its effectiveness means that the cost is offset by savings in the cost of diagnosis. The authors estimated that with an 85% detection rate, the cost to the NHS would be £15,300 per Down's pregnancy for the integrated test, compared with £16,800 using the quadruple test alone. However, costs vary between hospitals. Healthcare professionals can test whether the savings would apply for their budgets on the Wolfson Institute's Screening Cost Calculator: www.smd.qmul.ac.uk/wolfson/screencost/.

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Other resources:
The Down's Syndrome Association