non-invasive pre-natal testing

When I first started doing non-invasive first trimester screenings 10 years ago, we were only able to take a sample of the mother’s blood and test for the presence and amount of pregnancy hormones hCG and PAPP-A. When taken in consideration together with the results of the nuchal translucency test - which measures the thickness of the baby’s neck - one can assess the risk that the baby has a chromosomal disorder such as Down Syndrome, Edward Syndrome or Patau Syndrome.

While these tests were great for being non-invasive (and therefore non-threatening to the baby), their accuracy is 90-91% and is dependent on the operator’s proficiency. Today, however, thanks to recent advances in medical science, we now have a new test that is both non-invasive as well as highly accurate.

This non-invasive form of prenatal screening is capable of isolating and assessing the baby’s DNA simply from a sample of the mother’s blood, allowing doctors to determine with 99% accuracy if a baby is likely to have any of the common chromosomal disorders. If the test result comes back positive, only then will a diagnostic test - such as Amniocentesis or Chorionic Villus Sampling (CVS) - need to be performed to confirm the results.

This remarkable development in screening technology allows us to perform a smaller number of diagnostic tests on pregnant mothers overall. This is a great thing as both Amniocentesis and CVS carries a small but non-negligible risk that the foetus may be lost. The aim is to reduce the number of diagnostic test that needs to be performed.

The only real downside to the test is its cost, which ranges from $1600 to $2200. This high cost is due to the fact that there are no local laboratories capable of running the tests: all blood samples must be couriered back to their home laboratories in the United States where the testing will be performed and the results couriered back to the doctor. This entire process takes about two weeks in all.

As this screening test can be performed as early as 10 weeks, the results will be available at 12 weeks. Gynaecologists & Obstetricians will also be able to perform a early fetal anomaly scan including assessing the nuchal translucency at 12 weeks, allowing the doctor to assess the risk of both chromosomal disorders as well as any structural abnormalities by the end of the first trimester. With this new approach, more couples will be happily reassured without the need for invasive testing and they can then look forward to the rest of the pregnancy with greater confidence.

Dr Ann Tan
Dr Ann Tan, PBM
Obstetrician & Gynaecologist
MBBS (S'PORE), MRCOG (LONDON),
M MED (O&G) FAM (SINGAPORE)
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