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• 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) (see Genetics Fact Sheets 17A and 17B)
  • 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 (see Genetics Fact Sheet 17C)
  • Preimplantation genetic diagnosis (PGD) is used to test the embryo created via in vitro fertilisation (IVF) therapy prior to implantation (see Genetics Fact Sheet 18)
• 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

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 (see Genetics Fact Sheet 18)

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 17.1.

Barlow-Stewart K, Emery J, Metcalfe S. (2007).Testing and pregnancy. In: Genetics in Family Medicine: the Australian Handbook for General Practitioners. Biotechnology Australia, Commonwealth Department of Industry, Tourism and Resources

Gardener, RJ and Sutherland GR. (2004). Chromosome abnormalities and genetic counselling, New York: Oxford University Press

Hook EB. (1981). Rates of chromosomal abnormalities. Obs Gyn 58 282-285

Morris JK, Mutton DE and Alberman E. (2002). Revised estimates of maternal age specific live birth prevalence of Down's syndrome. Journal of Medical Screening. 9, 2-6

The Royal Australian and New Zealand College of Obstetricians and Gynaecologists [online]. Available from: www.ranzcog.edu.au. [Accessed June 2007]