Produced by the Centre for Genetics Education.
Important points
• There are a number of different prenatal tests and procedures available to assess the development of the baby. Each has advantages, disadvantages and limitations
• There is no test that gives a 100% guarantee of a healthy baby. The tests give some information about the baby’s health. They do not find all potential health problems
• Counselling before a test is done, will help the woman decide which test, if any, is best for the woman and the baby
• Each prenatal test is done at a certain time during the pregnancy starting at 8-10 weeks and going through to 20 weeks and include:
– Prenatal screening tests that may identify a baby as being at an increased risk of having a particular problem. All pregnant women, regardless of their age or family health history, may choose to have one of these prenatal screening tests that include ultrasound; early pregnancy (first trimester) screening: nuchal translucency ultrasound with or without testing of the mother’s blood; second trimester screening: testing of the mother’s blood (maternal serum testing)
– Prenatal diagnostic tests that are used to see if the baby actually has a particular problem. Even if the test result is normal, however, the baby could still have some other problem. Prenatal diagnostic tests include ultrasound; chorionic villus sampling (CVS); amniocentesis; cordocentesis
– Preimplantation genetic diagnosis (PGD) is used to test the embryo created via in vitro fertilisation (IVF) therapy prior to implantation
• The consideration of prenatal diagnostic testing is indicated when
– There is a close relative or a previous child with a serious condition
– One of the partners in a couple has a serious condition that may be passed on to a baby
– Both parents are ‘carriers’ of the same faulty gene
– The mother is in her mid-30s or older (not necessarily her first pregnancy) as there is an increased risk for having a baby with chromosomal problems due to more or less than the usual number of chromosomes
– There has been exposure to some chemical or other environmental agent
– The results of screening tests such as ultrasound or first and second trimester screening tests have determined that the baby is at increased risk for a particular genetic condition in this pregnancy
• Prenatal screening tests are available to pregnant woman of all ages
• Genetic counselling is available if the baby is found to have an increased risk for a chromosome problem following a prenatal screening test, or is found to have a problem following diagnostic testing, and will provide an opportunity to discuss what the result means for the parents and the family, and provide support for their decision-making
Every couple wants to have a healthy baby. For most couples, this wish will come true. There are, however, some couples whose baby may have a serious physical or intellectual problem.
There are a number of different prenatal (meaning before birth) tests and procedures available to assess the development of the baby. Each has advantages, disadvantages and limitations. This information is for those who are
• Planning a pregnancy
• Already pregnant and want information about these tests
There is no test that can guarantee a baby will be healthy
The prenatal tests described in this series of Fact Sheets give some information about the baby’s health. They do not identify all potential health problems. The woman can choose whether she wants any testing at all or which tests are best for her after talking to the doctor, midwife or genetic counsellor.
• Some people decide to have prenatal testing because they want to know if their unborn baby has a condition that causes serious physical and/or intellectual problems
• Some people decide not to have prenatal testing
The importance of counselling in association with prenatal testing
Counselling before any prenatal test is done, whether it is a screening test or a diagnostic test, is strongly recommended. It provides an opportunity to discuss:
• How and when the tests are done
• The advantages and disadvantages of each test
• Any risks to the baby that may result from each test
• Any further testing which the woman may be offered after she receives the result
• What this further testing will mean for the woman and the baby
Counselling before a test is done will help parents decide which test, if any, is best for the woman and the baby.
If the baby is found to have an increased risk for a chromosome problem following a prenatal screening test or is found to have a problem following diagnostic testing, professional genetic counselling will provide an opportunity to discuss:
• What the result means for the parents and the family
• The options available to the parents at this time
• Whether they wish to have further testing if available
• The advantages and disadvantages of any further testing that is offered
• What course of action the woman and her partner wish to take
Support will be offered to the woman and her partner at this time, no matter what they decide to do.
What types of prenatal tests are available in Australia?
a) Prenatal screening tests may identify a baby as being at an increased risk of having a particular problem. Screening tests cannot determine if the baby definitely has a problem but may indicate that further testing needs to be considered (diagnostic testing). All pregnant women regardless of their age or family health history may choose to have one of these prenatal screening tests. Prenatal screening tests include:
• Ultrasound
• Early pregnancy (first trimester) screening: nuchal (pronounced new-cal) translucency ultrasound with or
without testing of the mother’s blood
• Second trimester screening: testing of the mother’s blood
(maternal serum testing)
b) Prenatal diagnostic tests are tests done to see if the baby actually has a particular problem. Even if the test result
is normal, however, the baby could still have some other problem. Prenatal diagnostic tests include:
• Ultrasound
• Chorionic villus sampling (usually simply called CVS)
• Amniocentesis (pronounced am-nee-o-cent-ee-sis)
• Cordocentesis
c) Preimplantation genetic diagnosis (PGD) that tests the embryo created with the use of in vitro fertilisation (IVF)
therapy prior to implantation
When are prenatal tests done during pregnancy?
The different prenatal tests are only able to be done at certain times during the pregnancy starting at 8-10 weeks and going through to 20 weeks. A timeline for testing is shown in Figure 1.
Figure 1. Time line of prenatal testing including prenatal screening and diagnostic testing
What are the reasons for considering having a prenatal test?
Prenatal screening tests are available to pregnant women of all ages and, in particular when:
• There is a close relative or a previous child with a serious genetic condition
• One of the partners in a couple has a serious condition that may be passed on to a baby
• One or both parents are known ‘carriers’ of a particular faulty gene
• The mother is in her mid-30s or older (not necessarily her first pregnancy) as there is an increased risk for having a baby with chromosomal problems due to more or less than the usual number of chromosomes; eg. Down syndrome (see Figures 2 and 3)
• There has been exposure to some chemical or other environmental agent
• The results of screening tests such as ultrasound or first or second trimester screening may determine that the baby is at increased risk for a particular genetic condition in the pregnancy
Figure 2: Chance of having a live-born baby with Down syndrome (trisomy 21) according to the mother’s age at the time of delivery of the baby.
Figure 3: Chance of having a live-born baby with any chromosomal abnormality according to the mother’s age at delivery.
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