Diagnostic Tests

Invasive Diagnostic Prenatal Tests

Prenatal Diagnostic web v1

What happens during an invasive test?

  • The two most common invasive prenatal tests are; chorionic villus sampling (CVS) and amniocentesis.
  • These are both outpatient procedures and are performed within a couple of minutes.
  • No general or local anaesthetic is applied and the you are awake during the procedure.
  • Feelings of discomfort, cramping or pinching may be experienced, but little or no pain.

What is to expect after having an invasive procedure?

  • For a day or two after the procedure you should refrain from heavy lifting, intercourse and strenuous exercise.

What are the risks associated with an invasive diagnostic test?

  • Risk of miscarriage.
  • Some women experience cramping or spotting after the procedure. Although common, if concerned, you should contact your doctor.
  • Complications may include leakage of amniotic fluid, fever, or infection.  If this occurs you should consult with your doctor.

When will I get my results?

  • Certain conditions (Down syndrome, trisomy 13, trisomy 18 and sex chromosome abnormalities) can be identified within three days of having a CVS or amniocentesis.
  • For other specific / familial genetic conditions it can take a laboratory two to three weeks to provide a final result.

What happens if the result of the diagnostic test shows my baby has a problem?

You can discuss the result with your genetic counsellor who will provide you with information about the cause, prognosis and future management of the condition.  Your genetic counsellor will offer support by discussing the various options available, including their benefits and limitations, thereby helping you make informed personal decisions.


CHORIONIC VILLUS SAMPLING

What is Chorionic Villus Sampling (CVS)?

  • A thin needle, guided by ultrasound, is inserted through the abdomen to take a sample from the placenta (chorionic villus cells).
  • The procedure is performed in the doctors’ rooms. Usually by a fetal medicine specialist.
  • This sample is then used to test for for chromosome abnormalities and/or specific genetic conditions.

When should the test be performed?

11 to 14 weeks gestation.

What does the test detect?

Detects with certainty the presence of specific chromosomal abnormalities and genetic conditions.

What are the benefits of CVS?

  • Certainty of results.
  • An early result allows women to make decisions in the early stages of pregnancy.

What are the limitations of CVS?

CVS cannot diagnose ALL birth defects or genetic conditions only those that are being tested.

What are the risks associated with having a CVS?

  • There is a miscarriage risk of less than 2%.
  • A different diagnosis is made than that which was suspected.

AMNIOCENTESIS

What is an amniocentesis?

  • A needle, guided by ultrasound is inserted through the abdomen into the uterus to take a small sample of amniotic fluid that surrounds the baby.
  • This sample is then used to test for for chromosome abnormalities, neural tube defects and/or specific genetic conditions.

When should the test be performed?

Ideally between 16 and 20 weeks gestation, it depends on the treating physician.

What does the test detect?

  • Detects the presence of specific chromosomal abnormalities and genetic conditions.
  • Levels of alpha-fetoprotein levels (AFP) in the amniotic fluid can be measured and used to determine the presence of open neural tube defects, such as spina bifida.

What are the benefits of amniocentesis?

Certainty of result.

What are the limitations of amniocentesis?

An amniocentesis cannot diagnose ALL birth defects or genetic conditions only those that are being tested.

What are the risks associated with having an amniocentesis?

  • There is a miscarriage risk of less than 1%.
  • A different diagnosis is made than that which was suspected.
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