Down's test revamp urged

Health officials and doctors are considering a revamp of Down syndrome screening, which relies on a weak test and leads to abortions of fetuses without the condition.

They are evaluating widespread use of blood tests to improve the safety and effectiveness of testing during pregnancy for the chromosome disorder. At present screening is based mainly on ultrasound scanning of the fetus' neck. Women at risk are offered amniocentesis - in which a needle is inserted into the uterus - although the preceding scan is not considered highly sensitive on its own.

The Health Ministry wants to reduce the use of amniocentesis, which it estimates is done on 5 per cent of pregnant women, because it causes miscarriages in 0.5 to 1 per cent of cases.

Auckland University's professor of maternal fetal medicine, Peter Stone, wants the immediate introduction of a suite of blood tests in the first and second thirds of pregnancy and their eventual co-ordination with ultrasound scanning. This would produce a very high detection rate and a low (0.9 per cent) rate of false positive results, he says.

"International evidence shows that the current New Zealand situation can be dramatically improved and at present it is probable more harm than good is being done," he wrote in the New Zealand Medical Journal.

He suggested that testing by invasive methods - such as amniocentesis after screening with age and/or ultrasound - meant that "more unaffected pregnancies are likely to be being lost than abnormal ones are being detected. This must surely be an unsustainable and undesirable situation".

New Zealand's incidence of Down syndrome rose from 0.87 per 1000 live births in 1996, to 1.48 (80 Down babies) in 2002.

At a ministry symposium on screening in Wellington today British expert Professor Nicholas Wald will advocate the use of the five screening blood tests with neck scanning at the 11-week point in pregnancy.

Professor Wald, of the London School of Medicine & Dentistry, said that, with a woman's age, these tests could identify 85 to 90 per cent of affected pregnancies. These women could then be offered amniocentesis, a highly accurate test.

This system, which was being adopted in Britain, could reduce the proportion of pregnant women having an amniocentesis to 1 to 2 per cent.

The ministry's chief adviser on child and youth health, Dr Pat Tuohy, said it was considering switching to this system as part of a review of maternity services.

If a decision was made to proceed with financing the blood tests, they could start next year.

"We are not considering that we should set up a national screening programme, although that's a possibility in future."

Professor Wald said the new system might not affect the incidence of Down syndrome births; reducing the rate was not the intention.

"It's to give parents the choice as to whether they could avoid having a baby with Down syndrome."

He said 5 to 10 per cent of women who knew they were carrying a baby with the condition chose not to end the pregnancy.

The Down Syndrome Association's executive officer, Zandra Vaccarino, said yesterday it supported making the testing safer and more effective. People must not be pressured into having the tests and if the tests were positive they should be given reliable information and put in touch with the association.

DOWN SYNDROME

The condition

* Caused by an extra chromosome, which results in intellectual disability and an increased risk of some physical problems, including heart disease.

* Linked to increasing maternal age. Risk rises steeply after 35.

The tests

* New Zealand's main Down's screening test in pregnancy is ultrasound scanning, which measures the thickness of fluid space at the back of the fetus' neck.

* For those at greater risk, the main diagnostic test is amniocentesis. Through a needle inserted into the uterus, a sample of the fluid around the fetus is taken for laboratory testing.