Obstetrician, Gynaecologist & Fertility Specialist Brisbane

Dr Robert Watson MBBS, FRANZCOG

North West Medical Centre

125 Flockton St
Everton Park, QLD 4053
Telephone: 07 3353 4710
Fax: 07 3353 1258
Email: reception@drbobwatson.com.au
QFG Website

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Screening for Down syndrome and other Foetal Anomalies

NIPT blood test
Over 10 weeks. This test is 99.5% accurate.  This blood test from the mother examines tiny fragments of foetal DNA shed from the placenta into the maternal circulation.  This new test is not covered by Medicare and costs approximately $400.  It is extremely accurate for diagnosing abnormalities of chromosomes 21 (Down Syndrome), 13, 18 and the gender chromosomes.  Results take approximately 14 working days.  Three percent of tests are uninterpretable due to technical problems.
This test has been extended to include “Microdeletions”.  These conditions are individually rare but collectively can result in children with severe physical and intelectual disabilities.  The 22q11 deletion syndrome, Angelman syndrome, Cri-du-chat syndrome and Prader-Willi syndrome are tested. It costs an additional $200.

NT Scan
Twelve to 13 weeks.   This consists of a blood test for hormone levels and an ultrasound scan through the abdomen which examines the thickness of the skin fold over the baby’s neck.  This test gives a probability of Down syndrome. This test diagnoses eight or nine out of ten Down’s pregnancies and misses one or two out of ten.  One in 20 women are told their test is high risk when the pregnancy is normal.  If the risk is elevated, usually women proceed to an amniocentesis or CVS. This ultrasound also gives us a limited early opportunity to check the baby’s anatomy.

Chorionic Villus Sampling (CVS)
Twelve to 13 weeks.  A needle is passed through the abdominal wall into the placenta.  The placenta is biopsied and tissue is sent for immediate chromosomal analysis. This test is 99.5% accurate but carries a 1:70 chance of causing a miscarriage.  All chromosomes (including Chromosome 21 - Down Syndrome) are tested.

Amniocentesis
Sixteen weeks.    A needle is passed into the fluid around the foetus through your abdominal wall.  This fluid is sent for chromosome analysis.  Down syndrome can be mostly excluded within 24 hours.  The full chromosome report can take up to two weeks.  This test is 100% accurate but carries a 1:200 risk of causing a miscarriage.

Morphology scan
Nineteen weeks.  The morphology scan is routine and recommended for every pregnant woman.  This checks the baby’s anatomy and position of the placenta.  This scan is very good (but not perfect) at excluding abnormalities of the heart, kidney, brain and spine, etc.

Before considering tests for foetal anomalies and chromosome abnormalities, one should always consider whether obtaining this information is really necessary and whether it would affect the outcome of your pregnancy.  Every pregnancy carries a small risk of foetal anomalies.  Some women are at more risk than others because of their age or previous family history.  When considering screening tests, one should always consider the probability of an anomaly and weigh this against the risks of the procedure (miscarriage, in the case of amniocentesis or CVS) and the emotional trauma associated with a “false positive” or abnormal results in the presence of a normal foetus.
Your choice of anomaly screening depends on your own circumstances.  Young women may choose to have no screening.  Women who would never terminate a pregnancy on religious or ethical grounds should also consider having no testing at all. 

Please do not hesitate to discuss the options and your concerns with Dr Watson.

TEST

GESTATION

DIAGNOSIS RATE

FALSE POSITIVE

COST* approx

NIPT

After  10 weeks

995/1000

5/1000

$730

NT Scan

12-13 weeks

8-9/10

1/20

$350

CVS

12-13

995/1000

1/1000

$350

Amniocentesis

After 16 weeks

100%

0%

$350

TEST
NIPT
GESTATION
After  10 weeks
DIAGNOSIS RATE
995/1000
FALSE POSITIVE
5/1000
COST* approx
$400
TEST
NT Scan
GESTATION
12-13 weeks
DIAGNOSIS RATE
8-9/10
FALSE POSITIVE
1/20
COST* approx
$350
TEST
CVS
GESTATION
12-13
DIAGNOSIS RATE
995/1000
FALSE POSITIVE
1/1000
COST* approx
$350
TEST
Amniocentesis
GESTATION
After 16 weeks
DIAGNOSIS RATE
100%
FALSE POSITIVE
0%
COST* approx
$350

*out of pocket cost