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 $730.  It is extremely accurate for diagnosing abnormalities of chromosomes 21 (Down Syndrome), 13, 18 and the gender chromosomes.  Results take approximately 14 working days.  Five percent of tests are uninterpretable due to technical problems.
Recently this test has been extended to include “Microdeletions”.  These conditions are individually rare but collectively can result in children with long term health problems.  These conditions include 22q11 deletion syndrome, Angelman syndrome, Cri-du-chat syndrome and Prader-Willi syndrome.  This test costs approximately $730, including the Down’s screening above.

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.  If Down syndrome is considered high risk (that is more than 1:200), a woman may choose to have a more accurate test.  This is a screening test.  It 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 chromosomes are actually normal.  If the risk is elevated, usually women proceed to a more accurate test.  That test has traditionally been an amniocentesis or CVS.  More recently, women are choosing to have the NIPT blood test as follow-up.  This ultrasound also gives us a limited early opportunity to check the baby’s anatomy.

Chorionic Villus Sampling (CVS)
Twelve to 13 weeks.  This test consists of a needle 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.  Apart from Down syndrome, tests can be performed for many other chromosomal abnormalities, if necessary.

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 almost routine and is 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 (for Down syndrome) or previous family history.  When considering screening tests, one should always consider the underlying 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.  The most popular test for Down’s screening is an NT scan at 12 weeks.  This test can cost up to several hundred dollars and is moderately accurate.  Older women, who have a higher risk of Down syndrome, may choose the NIPT blood test as the first line test.  Others have the NIPT if the NT scan suggests a higher risk.

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
$730

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