Screening tests in the first 3 months of pregnancy
You may wish to find out early in your pregnancy if your baby is at increased risk of a serious health condition by having a screening test in your first trimester (the first 3 months of pregnancy).
The test combines results from a blood test and an ultrasound to assess the risk of having a baby with Down syndrome. This test can detect some other abnormalities and may also tell if you have a multiple pregnancy, for example twins. The screening test does not usually detect spina bifida.
The first trimester screening test is done between 9 weeks to 13 weeks 6 days of your pregnancy.
This test, or the second trimester screening test (done in the second 3 months of pregnancy), can help you decide if you want a diagnostic test.
As both the first and second trimester tests screen for similar conditions it is not recommended that you have both. Many women have their screening test as early as possible, in their first trimester, to find out if there could be a problem.
However if you are too late for the first trimester test or it is not offered in your area you may find a second trimester test valuable.
How is the test done?
The first trimester test involves 2 measurements:
- A sample of your blood is taken at a pathology collection centre between 9 weeks to 13 weeks 6 days of your pregnancy, but ideally between 9 to 12 weeks. This test is used to check the levels of 2 hormones in your blood that change during pregnancy (free B-hCG and PAPP-A). Changes in these levels can indicate a serious chromosomal condition.
- An ultrasound is done between 11 weeks to 13 weeks 6 days of pregnancy, ideally at 12 to 13 weeks. The ultrasound allows the thickness of fluid in an area behind the baby’s neck to be measured. This area, known as nuchal translucency, is often larger in babies with Down syndrome. The person performing the ultrasound will also take some measurements to calculate your developing baby’s gestational age (age in weeks and days).
A computer program then combines these test results plus your exact age, weight and your baby’s correct gestational age, to identify the risk of your baby having Down syndrome, Trisomy 13 and Trisomy 18.
Your results should be available within a week. They will be given to your doctor who will also tell you if a physical abnormality has been found during the ultrasound examination.
Understanding the results
The results are given as the risk or chance your baby will be affected:
- ‘Not at increased risk’ means your risk of having a baby with Down syndrome is very low (the risk is less than 1 in 300, or 0.0033 per cent). A different birth defect could still be present, but this risk is also low.
- ‘At increased risk’ means your risk of having a baby with Down syndrome is greater than 1 in 300 (the risk lies between 1 in 2 and 1 in 300). If your baby is at increased risk, a diagnostic test will be offered to confirm whether or not your baby has Down syndrome.
Limitations of the tests
One in every 25 women tested will be told they are at increased risk. This does not mean there is definitely something wrong with your baby, but you may wish to think about having further diagnostic tests.
There may be costs for these screening tests. You may be able to claim part of this cost from Medicare (external site). Please ask when you book your appointment about the costs and any rebates available.
- Screening tests are routinely done in the first trimester (first 3 months of pregnancy) or second trimester (second 3 months of pregnancy).
- If your screening test results shows your baby is at increased risk you may wish to have diagnostic tests. Diagnostic tests confirm the presence of a condition and are very accurate.
- Some diagnostic tests can increase the risk of pregnancy loss (miscarriage).
- Screening and diagnostic tests during pregnancy cannot detect all health conditions.
Office of Population Health Genomics
This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.