Overview

Maternal serum screening is a blood test available to pregnant women who want to know about their chance of having a baby with a chromosome condition, such as Down syndrome. Serum screening also provides additional information about pregnancy health.

What is this test?

Maternal serum screening is a type of prenatal screening test. There are two serum screening tests available to all women; combined first trimester screening (cFTS) and second trimester screening (2TMSS).

These screening tests give an estimate of the risk that a pregnancy is affected by a chromosome condition or certain developmental problems, but do not provide a definite diagnosis. They are used to separate women into ‘high chance’ or ‘low chance’ categories.

Combined first trimester screening is performed between 10 and 14 weeks gestation. This test combines a number of different measures together to provide an estimate of the chance that a pregnancy is affected by a chromosome condition, such as Down syndrome.

These measures are:

  • Blood, taken between 9-13 weeks gestation to measure two chemicals called PAPP-A and
    free beta hCG.
  • A nuchal translucency ultrasound (NT scan) at 11-13 weeks.
  • Maternal age, weight and gestation.
  • +/- nasal bone in some cases.

Combined first trimester screening can also provide useful information for the management of a pregnancy, such as risk factors for early onset pre-eclampsia.

Second trimester maternal serum screening is a single blood test, that is performed between 14-20 weeks gestation (best between 15-17 weeks). This test measures four chemicals: alpha-feto protein, unconjugated estriol, free beta hCG and dimeric inhibin A.

These results are combined with maternal age, weight and gestation to provide an estimate of the chance a pregnancy is affected by a chromosome condition, such as Down syndrome as well as neural tube defects like spina bifida.

What conditions does this test look for?

Maternal serum screening is used to help identify pregnancies that have an increased chance of being affected by a chromosome condition. These conditions are caused by an extra or missing chromosome in the developing baby.

Combined first trimester screening looks for Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13).

Second trimester maternal serum screening looks for Down syndrome, Edwards syndrome and neural tube defects such as spina bifida.

How do I arrange a test?

Patients will require a signed request form from their GP for maternal serum screening.

Depending on the gestation of the pregnancy, combined first trimester or second trimester screening will be performed. Bloods for serum screening can be taken at certain pathology collection centres. Your doctor will instruct you which collection centres are sending maternal serum screening to VCGS. No special preparation is required before this test.

For combined first trimester screening, a detailed ultrasound is also required. Specialist ultrasonographers are recommended. Your doctor will help organise your ultrasound.

Frequently asked questions

Should I have both combined first trimester screening and second trimester maternal serum screening?

No. There is no need to have both first and second trimester maternal serum screening.

What’s the difference between maternal serum screening and non-invasive prenatal testing (NIPT)

Both NIPT and maternal serum screening offer high quality screening options to determine if a pregnancy has an increased chance of a chromosome disorder such as Down syndrome. NIPT is a more accurate screening test than maternal serum screening for the indicated chromosome conditions but it is also more expensive. Maternal serum screening still provides a highly accurate screening test and can provide additional information about the health of the pregnancy, in particular, the risk of pre-eclampsia.

Because maternal serum screening has a lower cost and is partially covered by Medicare, many women choose to have combined first trimester screening first, then follow up with NIPT if they get a ‘screen positive’ result.

How accurate is maternal serum screening?

Combined first trimester screening will accurately predict 90%, or 9 out of 10 pregnancies affected by Down syndrome.

Second trimester maternal serum screening will accurately predict 75-80%, or 8 out of 10 pregnancies affected by Down syndrome.

As with all screening tests, there can be false positive and false negative results. Screening tests are not diagnostic – they are never 100% accurate. Depending on your screening result, diagnostic testing may be offered to confirm the result.

How much does maternal serum screening cost?

Out of pocket costs will vary depending on where you get your blood collected, where the ultrasound is performed and whether you are a public or private patient. An approximate out of pocket cost for serum screening after Medicare is $70. This does not include the cost of the ultrasound required for cFTS.

How will I get my results?

Serum screening results will be faxed and delivered electronically (where available) through to your referring doctor.

Combined first trimester screening results available 5 days from the time the laboratory receives the ultrasound information. This can be two weeks from when blood was taken.

Second trimester screening results usually available within one week of having your blood sample taken.

What do my results mean?

Maternal serum screening results are reported as ‘screen negative’ or ‘screen positive’. A result might also be reported as a number, for example, 1 in 300.

Screen negative or low chance: this means it is unlikely your pregnancy is affected by one of the conditions that were being screened for. False negative results can occur and there is no screening test that can rule out all possible conditions. A screen negative result means that diagnostic testing will not usually be offered.

Screen positive or high chance: a screen positive result does not mean a pregnancy is definitely affected by one of the conditions being screened for; it means the pregnancy has an increased chance of having a condition. In most cases, the pregnancy will not be affected.

A diagnostic test is the only way to confirm if a condition is present or to provide reassurance that the pregnancy is not affected. If you receive a screen positive result, you will be offered diagnostic testing.

What happens after a screen positive result?

If you receive a screen positive result, one of the specialist VCGS genetic counsellors will contact your referring doctor to discuss further testing options, such as diagnostic testing. Another option is to have a non-invasive prenatal test (NIPT) like percept™. These options should be discussed with your doctor.

Screening tests do not provide a definitive (yes or no) answer. Diagnostic testing is the only way to confirm the presence of a condition or to reassure a pregnancy is not affected.

I wish to speak to a genetic counsellor about maternal serum screening.

If you have more questions about maternal serum screening please contact one of our genetic counsellors: (03) 9936 6402.

I’ve received an invoice from VCGS – how do I pay?

After testing is complete, patients will receive an invoice. This can be paid by phone using BPAY or credit card, or by mail using a money order or cheque. Payment methods are detailed on the invoice.

To claim the Medicare rebate, take the receipt of payment to a Medicare centre or online. Once processed, Medicare will send you your rebate.

If you wish to speak with someone about your invoice: Free Call: 1300 557 779.