New test for baby's DNA risk available in Singapore

PHOTO: New test for baby's DNA risk available in Singapore

SINGAPORE - Expectant mothers now have another option in testing for the likelihood of their child having Down syndrome or some other chromosomal abnormalities.

Unlike the existing first trimester blood test which analyses the mother's hormones, this new test analyses small foetal DNA fragments in the mother's blood and is more accurate.

Like current tests, it is done mainly to check for Down syndrome, the most common chromosomal abnormality, though it also checks for other abnormalities such as Edwards syndrome.

Down syndrome, also known as trisomy 21, is marked by mild to moderate intellectual disability and other health problems. Edwards syndrome is a genetic disorder, also known as trisomy 18, which causes major physical abnormalities and severe mental retardation. Most foetuses die before birth while those who survive rarely do so beyond a year.

Currently, expectant mothers go through a non-invasive screening test - which comprises a blood test and an ultrasound scan - to determine the chances of their child getting Down syndrome and some other chromosomal abnormalities.

The ultrasound scan, called a nuchal scan, measures the translucent space in the tissue at the back of a developing baby's neck between 11 and 14 weeks. Babies with abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, causing this clear space to be larger than average.

Assessed together, the nuchal scan and blood test are approximately 90 per cent sensitive, said Dr Ann Tan, a gynaecologist and obstetrician who chairs the obstetrics and gynaecology speciality interest group of Mount Elizabeth Hospital. The group comprises gynaecologists and obstetricians who meet the hospital management quarterly to discuss hospital issues.

A higher detection rate

A higher detection rate

The new foetal DNA test, called MaterniT21 Plus, has an even higher detection rate than the current first-trimester screening.

"With the new test, we're looking for the baby's DNA and not the mother's hormones. The accuracy rate is nearly 99 per cent," said Dr Tan.

Expectant mothers can do the new test as early as the 10th week of pregnancy.

These screening tests are usually done as early as possible, in case there is a need to terminate the pregnancy.

If the tests show that the mother is at high risk of giving birth to a baby with Down syndrome, she will be offered a definitive test, such as amniocentesis, to confirm the results, before deciding whether to abort the baby.

Amniocentesis is an invasive procedure that is usually done between the 16th and the 20th week of pregnancy and carries a risk of miscarriage of around 0.3 per cent, said a spokesman for KK Women's and Children's Hospital (KKH).

Parkway Health Laboratory, the exclusive provider of the new test, launched it on April2. So far, 32 patients have taken the test, the company said.

Blood samples taken for this new test are analysed at the Sequenom laboratory in the United States and the results made available in about 10days to two weeks, said Dr Tan.

Sequenom is the San Diego-based life-sciences company that created the test, which is recognised by the American Congress of Obstetricians and Gynaecologists. Here, Parkway Health Laboratory is providing the frontline services such as the administrative support.

Be aware of limitations

Be aware of limitations

The new test should not replace the first trimester blood test and nuchal scan, said Professor George Yeo Seow Heong, head and senior consultant at the department of maternal foetal medicine at KKH.

It has limitations in that it cannot detect any structural birth defects. An integrated approach that includes an ultrasound scan will allow for the detection of more chromosomal disorders and structural abnormalities, especially the common congenital heart diseases, he said.

What the new test can do, he said, is to further narrow down the number of patients who require an invasive procedure for the detection of Down syndrome.

Dr Tan of Mount Elizabeth Hospital is advising a two-level screen.

She said: "I believe that for most mothers, the current first-trimester screen is still a good test to do as it can give up to 95 per cent sensitivity... and there is the additional benefit of the ultrasound examination of the foetus to exclude structural abnormality."

She added: "You do the current blood test first and if you are not satisfied with your results but do not desire an invasive test, you can then opt to do the new test."

This is particularly so for those with a moderate risk score, showing a one out of 250 to one out of 1,000 chance of having a Down syndrome child, she said.

For mothers who choose the new blood test, a nuchal scan around 12 weeks is still recommended, she said.

Like the current first trimester blood test, the new test is for screening and not diagnosis, stressed both experts.

It is meant to help the expectant mother decide if she should go for further tests such as amniocentesis to find out if her baby carries the abnormality or not.

High price a drawback

High price a drawback

A drawback of this new test is the price tag. It costs approximately $3,000 whereas the cost of the first-trimester blood test and ultrasound scan amount to only around $315 at KKH or slightly more at private clinics.

Prof Yeo said: "Given the very high cost of this new test, a careful cost-benefit analysis is essential before it can be introduced in routine obstetric care.

"We are currently in the process of this evaluation and are working closely with the Ministry of Health to ensure patients' best interests."

Ms Mehwish Bader, 30, is among those who have gone ahead with the test.

Her first trimester screening showed that her foetus was at moderate risk of Down syndrome.

She recalled: "My husband and I discussed it. We thought very, very hard about it and decided to do the new test.

"We were going to keep the baby no matter what but the results would have helped us to prepare ourselves mentally."

Fortunately for her, the result of the new test showed that she is not at risk of delivering a Downsyndrome child.

joyceteo@sph.com.sg


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