During pregnancy, screening tests, scans and diagnostic tests can provide different kinds of information about your baby’s health and development. Screening estimates the chance of certain chromosome or genetic conditions, while diagnostic testing can look more directly for a particular condition.
Understanding why a test is being offered, what information it may provide, what it cannot tell you and what may happen after a result can help you decide what information you want during pregnancy.
A screening test estimates whether your baby has a lower or higher chance of particular conditions. It does not diagnose the condition.
A diagnostic test looks more directly for the chromosome or genetic condition being tested for and can usually provide a more certain answer. It does not test for every possible condition, and some results can still be uncertain or need further explanation.
If screening suggests a higher chance of a condition, you should be offered information about what the result means and the option to discuss diagnostic testing before making decisions based on the screening result.
Clinical information can help explain the finding, possible health needs and what is still uncertain. Condition-specific organisations can also provide lived-experience information about how the condition can affect people and families in everyday life. Experiences can vary, so this information should sit alongside advice about your individual pregnancy.
Combined first trimester screening uses a blood test and an ultrasound in early pregnancy to estimate the chance of certain chromosome conditions. The ultrasound can also provide other information about the pregnancy that may need further assessment.
Non-invasive prenatal testing, usually called NIPT, is a blood test that can be done from around 10 weeks of pregnancy. It looks at small fragments of DNA from the placenta that are circulating in the pregnant person’s blood and estimates the chance of certain chromosome conditions, including Down syndrome.
NIPT is a screening test, not a diagnosis. If the result shows a higher chance of a condition, you should usually be offered specialist information and the option of diagnostic testing.
NIPT does not screen for every genetic condition and does not replace pregnancy ultrasounds. Different providers offer different panels, so ask exactly what the test includes.
NIPT is not currently covered by Medicare and is usually paid for privately. Ask about the full cost before testing.
Second trimester maternal serum screening is a blood test usually done between 15 and 20 weeks of pregnancy. It estimates the chance of certain chromosome conditions, including Down syndrome and Edwards syndrome, and neural tube defects such as spina bifida.
It may be an option if first-trimester screening was not done. A Medicare rebate is available for the blood test, although other costs may still apply.
Ultrasound provides information about your baby’s growth and development. The detailed morphology scan is commonly performed at around 18 to 22 weeks.
Ultrasound can sometimes identify a finding that needs further assessment, whether or not you have chosen other genetic or chromosome screening. Further assessment may include more detailed imaging, specialist review or an offer of diagnostic testing.
Diagnostic testing may be offered when screening or an ultrasound raises a question, or when a particular genetic condition is already known to be relevant to the pregnancy. Whether to have diagnostic testing is a personal choice.
Chorionic villus sampling, usually called CVS, collects a small sample from the placenta for genetic or chromosome testing. It is usually performed earlier in pregnancy than amniocentesis.
Because the sample comes from the placenta, occasionally another test may be needed if the placental result does not clearly reflect the baby’s result.
Amniocentesis collects a small sample of the fluid surrounding the baby. It is usually performed from around 15 weeks of pregnancy. Cells in the sample can then be tested for the chromosome or genetic condition being investigated.
Both procedures are invasive and carry a small chance of pregnancy complications, including miscarriage. The clinician offering the procedure should explain the current evidence, the risks relevant to your pregnancy and what information the test may provide.
CVS and amniocentesis are ways of collecting a sample. The laboratory test performed on that sample depends on the question. This may include chromosome testing or chromosome microarray, a targeted test for a genetic change already known in the family, or, in some specialist situations, broader genomic testing. Not every test is suitable or available in every pregnancy. Ask exactly which laboratory test is being done, what it can and cannot detect, and whether an uncertain result is possible.
Tell your maternity or genetics team as early as you can and bring a copy of the genetic report if possible.
A general NIPT or chromosome test may not test for the specific genetic change known in your family. The genetics team may need to organise a test designed specifically for that family result before chorionic villus sampling or amniocentesis can answer the question.
YourChoice prenatal screening decision aid →
Centre for Genetics Education: Prenatal testing booklet (updated August 2026) →
Prenatal Screening Awareness: informed-choice and lived-experience resources →
Queensland Health Genomics Resource Hub: During a Pregnancy →
INTERNAL GAA LINK: Unexpected news during pregnancy →
