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Screening revolution: foetal blood test a breakthrough with disadvantages

“The capacity to genetically test foetuses has just taken off,”: Michael Chapman. Photo: Katheirne GriffithsFrom the moment a woman discovers she is pregnant her mind is cluttered with an endless stream of questions. Will the baby be healthy? Will it have a birth defect? Will the foetus live until full term?
Nanjing Night Net

But advances in genetic testing mean many of those fears and worries weighing down expectant mothers may soon rapidly diminish.

For more than 40 years pregnant women have only been able to peek at the foetal wellbeing and chromosomal make-up of their unborn child through invasive diagnostic tests such as amniocentesis or chorionic villus sampling, both of which are stressful and carry a one in 400 chance of miscarriage.

New genetic technology – known as non-invasive prenatal testing (NIPT) – can screen for foetal disorders with 99 per cent accuracy through a simple blood test which isolates the baby’s DNA from maternal blood. It is a ”revolution” in pre-natal screening, doctors say, which presents no risk to the woman and is, by some estimates, up to 10 times better at detecting an extra copy of chromosome 21, which causes Down syndrome and is the most common genetic disorder, occurring in about one in 700 births.

And the relative simplicity of the test is expected to vastly reduce the 9200-odd Australian women who undergo amniocentesis (at 15 weeks) and CVS (at 11 weeks) each year, procedures which involve inserting a needle into the the womb to extract fluid or taking tissue from the placenta.

”The capacity to genetically test foetuses has just taken off,” says Michael Chapman, head of obstetrics and gynaecology at the University of NSW. ”In my 30 years of practice, this test is the most exciting step forward I’ve seen.”

The convenience, however, comes at a cost and there are some significant drawbacks, doctors warn. Australian women must spend $500 to $900 for their blood sample to be sent to the US for analysis and face a two-week wait for the results.

From early next year, pathology company Victorian Clinical Genetics Services will make NIPT tests available within Australia, with the price to drop by about 20 per cent and wait time reduced by about five days.

And unlike amniocentesis or CVS, which can give information about all 46 chromosomes, the NIPT test only looks for the presence or absence of chromosomes 13, 18, 21 and determines gender.

”There are major disadvantages,” says Dr Philippa Ramsay, the director of women’s ultrasound practice Ultrasound Care.

”It should not replace the standard 12-week ultrasound because a blood test won’t tell you about structural development, like if there are two arms, two legs and if there’s a heart beating. There is also about a one in 1000 risk of over-diagnosis, or the test coming back with a false positive. In the case it’s positive result, a woman still needs an invasive test because despite the accuracy, the NIPT is not diagnostic.”

And in the same way medical advances have intensified the moral issues at end of life, improved accuracy and availability of genetic tests means ethical problems at the beginning of life are equally as troublesome. Are advances in genetic testing outpacing our ability to handle them? Will people use it to select the gender of their child? How much information about a foetus should a parent receive?

One of the major concerns, says Gavin Sacks, a fertility specialist at IVF Australia, is that NIPT is able to determine the sex of the baby at nine weeks. ”This could create social pressure. We never want the information to be abused so that women end up terminating unwanted sexes.”

Ramsay said the ability to sex-select in the first trimester ”could become a big problem in cultures where there is major pressure to have a son”.

Sacks also says some people do not believe in or want screening. He is also concerned that the new test focuses on only a few chromosomal abnormalities.

Maternal foetal medicine consultant at Royal North Shore, Andrew McLennan, said in the past 18 months, the number of women having NIPT tests had jumped from about 10 a month to more than 250. Doctors estimate that within private practice about 10 per cent of women have the test. ”There is a real hunger for it in the community,” McLennan says. ”Especially with women who are over 36 or have an increased risk.”

A recent study of almost 2000 women, published in The New England Journal of Medicine, found that non-invasive tests could predict the likelihood of Down syndrome 10 times better than standard screening and were five times better at predicting Trisomy 18, also known as Edwards syndrome.

But McLennan warns that because of the new test only detects a handful of chromosomes, and based on the ethical concerns, women need to be properly counselled before having the NIPT. ”I’d hate to see it become a routine test,” he says. ”If that happens it would be a nightmare. At the moment, anyone can order these tests so appropriately qualified people need to discuss the implications and limitations with the patient. It may be a super-screening test but it definitely can’t tell you everything about the baby.”

This story Administrator ready to work first appeared on Nanjing Night Net.

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