Would you have the baby screening test that could wipe out every genetic defect?

Birth defects affect approximately one in every 46 babies born in the UK. Photo / iStock

A blood test that can screen an unborn child for all known genetic abnormalities - and may even be able to diagnose previously unknown ones - is to be offered to pregnant women by a private British clinic from next week.

Hailed as the most advanced foetal DNA test ever, the analysis will cost from £900 (NZD 2,120) and the US-based manufacturers claim trials have proven it is as accurate as the current best, and more invasive, tests offered on the NHS.

The MaterniT GENOME test can also be offered from ten weeks, whereas NHS pre-natal screening starts at 11 weeks. This involves an ultrasound scan that may flag up physical signs for concern, and other blood tests, after which other more invasive diagnostic tests may be carried out.

The human genome - the DNA code inside every cell that contains the "programme" for all our characteristics - has 46 chromosomes. Genetic abnormalities occur when part of a chromosome is damaged or missing, or when extra copies of the chromosome are present. More than half of all miscarriages in the early stages are due to such faults.

Birth defects affect approximately one in every 46 babies born in the UK, and numbers are rising due partly to the increasing numbers of older mothers. Age increases the risk: last year, more women between 30 and 34 gave birth than any other age group.

If a pregnancy is found to be at risk during the first NHS scan, women are then offered chorionic villus sampling (CVS) or amniocentesis to confirm a diagnosis.

But those tests involve passing a needle into the womb to take a sample from the placenta or amniotic fluid, and can lead to miscarriage in as many as one in 100 women, many of them carrying healthy babies.

The new screening, which looks for fragments of foetal DNA in the mother's blood, provides a way of finding out about even slight chromosomal changes, along with more established disabilities such as Down's syndrome, which affect one in 1,000 babies - without endangering the unborn child.

Because of its unparalleled accuracy, the test could reveal ultra-rare disorders - so-called SWAN conditions, which stands for Syndrome Without A Name - that affect up to 6,000 births each year and might typically be missed until far later in pregnancy.

However, disability rights campaigners and many in the medical community have voiced concern that the test will lead to a rise in abortions, and even terminations of healthy foetuses if parents are given the wrong information about the actual effects of a chromosomal abnormality.

Recent figures published by the Department of Health show that the number of abortions carried out because babies were found to have Down's or other serious disabilities has increased. Studies in the late 1990s found that when Down's is diagnosed in a foetus, between 80 and 90 per cent of parents choose to undergo a termination.

The new test is the latest evolution of non-invasive pre-natal tests (NIPTs), which have so far not been considered diagnostic, and only clarify the extent of the risk that the child will be born with a chromosomal problem. Previous versions also generally analysed only selected chromosome pairs linked to major abnormalities.

The MaterniT GENOME, made by Californian biotech company Sequenom, is the first to analyse all 46 chromosome pairs.

It means it can pick up unexpected changes to chromosomes known as microdeletions, duplications, translocations and other tiny alterations that can lead to birth defects.

The company also says it can analyse chromosomes at a more detailed level which is close to the resolution used to examine CVS and amniocentesis results.

This makes the test more accurate, according to Sequenom, and only one in 200 parents will be given a diagnosis in error.

Jane Fisher, director of the charity Antenatal Results and Choices, urged caution, saying: "It's a minefield. We're very much on the side of parents gathering information should they want it. But there have to be massive caveats - you must have genetic expertise on hand to help them understand information as it might flag up genetic variations of unknown significance.

"We've already had instances arising from private NIPT provision here where women are being given wrong information about the results from similar genetic tests, so it's already a problem.

"But such tests are often provided by private ultrasound clinics and they have absolutely no expertise in delivering complex genetic information. That's hard enough for clinical geneticists to do. So it's concerning that this will be available privately."

The test will be available initially at The Medical Chambers in Kensington, West London. It involves taking a sample of blood from the arm, which is sent to Sequenom's laboratories in America. The results are available on a secure server within a week.

Obstetric ultrasound specialist Dr David Nyberg, from The Medical Chambers, said: "The new test will pick up about 15 per cent more chromosomal issues than other available tests. There's always a danger we pick up something that doesn't mean anything, so in those circumstances we would check to see whether parents also have the genetic aberration or if it's new in the baby, and recommend genetic counselling.

"The bottom line is that, for the first time, we'll be offering a test which analyses all 46 chromosomes at a resolution that is similar to that of standard karyotyping [chromosome analysis] from amniocentesis.

"This is one of the biggest breakthroughs in foetal DNA testing ever. It has an unparalleled sensitivity of 99.9 per cent for multiple chromosomes and a false positive rate as low as 0.05 per cent. What this means is that the test will show a positive result for an abnormality where there isn't one in less than one in 2,000 mums. These rates are significantly better than anything previously used."

Professor Dennis Lo, professor of chemical pathology at the Chinese University of Hong Kong, pioneered NIPTs after discovering the presence of foetal DNA in maternal blood. He said it would remain necessary to have a CVS or amniocentesis to confirm the results from the new test.

"The DNA we detect in the blood plasma from the baby is released by the placenta," Prof Lo said.

"But the placenta could have a different chromosomal problem to the baby. And the more areas of the genome you target, the higher the chance there is of a false-positive happening."

The National Screening Committee is set to examine trial data to determine whether NIPTs could be available as standard across the NHS. The trial found they could save the NHS money because fewer invasive tests would be needed, and the lives of about 300 unaffected babies, who are miscarried following amniocentesis or CVS, could be saved.

William Welch, Sequenom's president and CEO, said: "As pioneers and innovators in non-invasive prenatal testing, we believe it represents a safe, cost-effective and meaningful breakthrough in NIPT, supporting physicians in providing superior prenatal care for their patients.''

It can't tell you how much love and joy you'll share

Alison Morley, 45, from Cheltenham, writes a blog at downrightjoy.com. She has two daughters, one of whom has Down's syndrome.

Alison says: '"his may be the most accurate screening ever, but it won't tell you, for example, how much joy your baby will give you or how happy they will be - whatever health problems they may have. It won't tell you how much you will love a child and how much that child will love you back.

"I found out during my pregnancy, at the first scan, that our daughter Hazel, now four, might have a heart defect and a syndrome such as Turner, or Down's.

"Statistically, I was told she was unlikely to survive beyond the 16-week mark, so I didn't opt to have any further diagnostic tests.

"But my faith meant that I would never have opted for a termination even though it was offered immediately.

"Hazel has brought more joy into our lives than we could possibly have imagined.

"Watching her riding a horse with the biggest smile on her face or hearing her laugh and giggle with her sister reminds me just how thankful I am for her.

"And, due to medical advances, she may well live a very healthy life well into her 60s.

"People with any kind of chromosomal condition are still people. I understand why many women want to take tests like these, but they should also be offered the chance to meet families affected by the conditions it flags up - then they can make an informed decision.

"Perhaps then they will see there is so much more to the child you are carrying than a syndrome."

- Daily Mail