Downs syndrome screening | NIPT | T21 | Glengarry Private
Combined 10 week blood test and 12-14 week ultrasound scan
Until very recently this was the best method of non-invasive testing. Unfortunately, 10-15% of Downs babies are missed with this method. Women with high-risk scores after scan & blood test will need 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. The 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. Partial Medicare rebates are available for this testing.
NIPT – the blood test – Harmony or iGeneScreen
This new NIPT test, available from several competing overseas providers, 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, as up to 50% of positive results are not correct. It is unknown how accurate it is at picking up rarer chromosomal abnormalities – this work is ongoing.
If you want this blood test, it’s done anytime after 12 weeks of pregnancy. The cost is about $500 and it takes about 2 weeks to be analysed overseas. There is no Medicare rebate.
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, but definitive results take 3 weeks. We expect this procedure to be much less needed over the next few years.
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 and are analysed very quickly. The subsequent miscarriage risk is higher than amnio, at about 1.5% overall. Again, we expect this procedure to be much less needed over the next few years.