Traditional Screening

Traditional screening tests measure protein and hormone levels in your blood and estimate the chance that the developing baby has a chromosome condition.

health care professional

Because it is a blood test, there is no risk to your pregnancy.

A screening test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome is available between weeks 10 and 14 of pregnancy. It’s called the combined test because it combines an ultrasound scan with a blood test. The blood test can be carried out at the same time as the 12-week scan.1

The screening test cannot harm you or your baby.1

The detection rate is when the test correctly indicates a high chance for a chromosome condition when it is present. The detection rate of traditional screening for the detection of Down syndrome has been shown to be 79%.2

Sometimes a test can indicate a high chance of a chromosome condition when the developing baby does not have it. This is called a false positive result. With traditional screening, about 1 in 20 women might receive a false positive result.2

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Screening Reminders

No screening test is designed to detect all possible conditions. Screening tests help identify pregnancies with an increased chance of certain chromosome conditions. With screening tests, false positive and false negative results will occur.

Women who have an increased chance on their screening test should consult a healthcare professional who can recommend additional invasive confirmatory or other testing.

Invasive Confirmatory Testing

Invasive confirmatory testing involves a procedure to obtain cells from the pregnancy for testing.3

Invasive confirmatory testing can give a definitive answer about most chromosome conditions in a pregnancy.

In most cases the result will let you know, one way or the other, whether your baby has the condition the test was looking for.

There are two types of invasive procedures, chorionic villus sampling and amniocentesis.

invasive confirmatory testing

Chorionic Villus Sampling (CVS)4

CVS is usually done from weeks 11 to 14 of pregnancy but can be done later.

This procedure removes a small sample of cells from the placenta using a needle (through the abdomen) or narrow tube (through the vagina).

All chromosomes within these cells are studied to see if there are any extra or missing.

CVS is estimated to give a definitive result in 99 out of every 100 women having the test.4

There is a small chance of miscarriage following the procedure.



Amniocentesis is usually done between 15 and 20 weeks of pregnancy, but it can be done later. Amniotic fluid contains cells from the developing baby, and a small sample of this fluid is removed using a needle that is inserted through the abdomen. All chromosomes within these cells are studied to see if there are any extra or missing.

Amniocentesis is estimated to give a definitive result in 98 to 99 out of every 100 women having the test.5

This procedure also carries a small chance for miscarriage.

There is a small chance of miscarriage following the procedure.


Why might I consider CVS or amniocentesis3

You may be offered a CVS or amniocentesis if:

  • There were unexpected findings at the time of your ultrasound scan
  • You have a higher chance screening-test result for Down’s syndrome or Edwards’ syndrome and Patau’s syndrome
  • You have had a previous pregnancy/baby with a genetic condition
  • You or your baby’s father have a family history of another genetic condition, such as sickle cell disease, thalassaemia major or cystic fibrosis

If offered a CVS or amniocentesis, it is your decision whether or not to have it. Your healthcare professional should help you make the decision that is right for you and support you in that decision.

  1. [Accessed December 2022]
  2. Norton et al. N Engl J Med. 2015 Apr 23;372(17):1589-97
  3. [Accessed December 2022]
  4. [Accessed December 2022]
  5. [Accessed December 2022]