Downs syndrome screening | NIPT | T21 | Glengarry Private

There are different methods of screening for chromosomal problems in babies – most commonly Down’s syndrome (trisomy 21)

Combined 10 week blood test and 12-14 week ultrasound scan

Until recently this was the best method of non-invasive testing. Unfortunately, 10-15% of Downs babies are missed with this method. Women undergo a blood test at 10 weeks & a scan at 12 weeks. An individualised risk is generated. Women with high-risk scores after scan & blood test can choose to undergo amniocentesis (a needle draws off some of the fluid round baby with a small risk of miscarriage) or CVS (a piece of placenta is removed – can be done earlier than amnio but higher risk of miscarriage) to make a diagnosis. This combined test is also used to indicate the possibility of rarer chromosomal problems eg. Edwards syndrome. Additional information gained during the blood test can give clues about the risk of premature birth or pre-eclampsia later in pregnancy, as levels of the placental PAPP-A hormone are reported. The scan part checks on early anatomy and spinal problems can be detected early. Partial Medicare rebates are available for this testing.

NIPT – the blood test – Generation 46 or Harmony

This new NIPT test analyses pieces of free DNA (from baby’s placenta) in the mother’s blood. It’s extremely accurate for ruling out the trisomies (extra chromosome) of Downs, Edwards & Patau syndromes. The chances of a baby with Downs being missed is very small. A recent study in the New England Journal of Medicine has shown superb performance. A confirmatory amniocentesis in positive cases only is needed. It is unknown how accurate it is at picking up rarer chromosomal abnormalities – this work is ongoing. Generation 46 is used for these rarer abnormalities and is offered for no extra cost.

If you want this blood test, it’s done anytime after 10-11 weeks of pregnancy. The cost is about $400 and it takes about 1 week to be analysed. There is no Medicare rebate.

Amniocentesis

Done for a variety of reasons, this simple procedure can be performed quickly without issue. The background risk of miscarriage is 1% and amniocentesis adds a little to this risk. Fluid is removed under ultrasound control from the sac away from the baby. This fluid can be analysed immediately for some conditions, but rare conditions and definitive results take 3-4 weeks. We expect this procedure to be much less needed over the next few years.

CVS

Can be done earlier than amniocentesis. This procedure uses ultrasound guidance to remove some placental tissue which is then analysed. Results are slightly less reliable than amnio but tissue is able to be analysed very quickly. The subsequent miscarriage risk is higher than amniocentesis, at about 1.5% overall. Again, we expect this procedure to be much less needed over the next few years.