Casey Anderson* was looking forward to her 12-week ultrasound, but her happy anticipation turned to distress when a nuchal measurement showed that her baby was considered high risk for Down syndrome.
“We went through 16 cycles of fertility treatment before falling pregnant, and I was devastated at the scan results,” Casey says.
On her doctor’s recommendation, she was booked in for an amniocentesis test. While Casey wanted confirmation of the scan results, the risk of miscarriage associated with invasive testing made her fearful
“After three years of trying to conceive, I was so afraid of having the amnio test and miscarrying,” she says. “The risk of my baby having Down syndrome was one in 271, while the risk of miscarriage with an amniocentesis was one in 300.
“The additional danger of leaking amniotic fluid and of contracting an infection also weighed heavily and I knew I couldn’t go to the appointment.”
Distraught, she spoke to a friend who mentioned a new prenatal test – the non-invasive prenatal test (NIPT).
Dr Bob Watson, a highly experienced obstetrician and senior specialist with Queensland Fertility Group, describes NIPT as “a fantastic test, and very exciting”. He recommends it to patients who require further diagnostic testing for Down syndrome and other chromosomal abnormalities, including Trisomy 13 (Patau Syndrome) and Trisomy 18 (Edwards Syndrome).
Unlike amniocentesis testing, in which a needle is inserted through the abdomen and into the uterus to take a sample of amniotic fluid, NIPT analyses foetal DNA in a pregnant woman’s bloodstream. It’s conducted by taking a small sample of blood from the mother’s arm, and is then sent off to be analysed for chromosomal abnormalities (the sex of the baby can also be determined).
Dads-to-be can also opt to supply a cheek swab, which may improve the performance of the test in certain circumstances.
“Currently, the main screening test for Down syndrome is the nuchal translucency scan, done at around 13-weeks gestation,” Dr Watson explains. “It predominantly consists of measuring the skin on the back of the foetal neck, and checking two proteins in the maternal blood, which vary if there is a chromosomal abnormality.
“The nuchal scan picks up eight or nine out of 10 Down’s pregnancies, which is far less precise than the 99.5 per cent accuracy of the NIPT test. Nuchal also has a 3-5 per cent false positive rate, which can lead to unnecessary worry and invasive diagnostic procedures like amniocentesis or chorionic villus sampling (CVS) for nothing.”
In order to perform the alternative CVS test, a needle is inserted through the abdomen. A fragment of the placental tissue is extracted and then analysed for chromosomal abnormalities and genetic conditions; due to its invasive nature, CVS has a one in 70 risk of causing miscarriage.
Because NIPT is a blood test, it has a zero per cent risk of miscarriage, can be done earlier in the pregnancy (from 10 weeks onwards), and is highly accurate. But it does have some limitations.
“It can’t be done in the case of a twin pregnancy because there are two placentas, or for women who used egg or embryo donation, as the different DNA would confuse matters,” Dr Watson says. “Sometimes there are not enough foetal fragments in the blood to make an assessment, and the test will have to be repeated around 5 per cent of the time,” he says.
Cost is a factor too, with the test ranging from $720 to $1500. There is currently no Medicare or private health insurance rebate available, although this may change.
Despite the cost, for the vast majority of women who require further testing, NIPT is a welcome option at a difficult time. Aside from reducing anxiety for many, it has additional advantages for women in remote and regional Australia.
“NIPT is a very good test for rural women because the blood test is a mechanised, automated process, while the nuchal scan requires a lot of training and there is an observer error margin – the accuracy depends on who does the scan and the equipment which is available and so on,” says Dr. Watson.
Whatever the location, there’s a two week wait for the results of NIPT, a period Casey describes as “the longest weeks of [her] life”. Thankfully the news for Casey was good, with her NIPT report showing an extremely low risk of Down syndrome, Trisomy 18 and Trisomy 13.
Casey and her husband have since welcomed a healthy baby boy and Casey says she would not hesitate to have the NIPT test again, or to recommend it to other women.
Dr. Watson is positive, too. “NIPT heralds a brave new world,” he says. “In a couple of months, NIPT will be expanded to include testing for Di George, Prader-Willi, Angelman and Cri du chat syndromes. Testing for haemophilia, cystic fibrosis and a range of other conditions could soon follow; what can be determined by gene sequencing can be done by NIPT.
“It provides invaluable information and offers women choices, which can only be a good thing."