SA Maternal Serum Antenatal Screening Program

Two request forms are required, one for the blood test (the SAMSAS request form) and one for the nuchal translucency ultrasound scan (which does not need to be performed on the same day as the blood test).

Blood Test

1. Provide the patient with the SAMSAS pre-test information sheet
2. Use a SAMSAS request form (see below to order SAMSAS request forms)
3. Complete ALL sections of the form
4. The test request is First Trimester Screen
5. Specify the ultrasound practice performing the nuchal translucency scan
6. Refer patient to the Privacy Disclosure on the SAMSAS request form
7. If performing blood collection on site, the sample type is 5-10 ml clotted blood sample (serum). Send the blood specimen to SA Pathology.

Ultrasound

1. Complete an ultrasound request form, specifying “risk of fetal abnormality”; and "Copy to SAMSAS".
2. The fetus must be 11w0d – 14w0d gestation at time of scan.
3. Refer patient to book a Nuchal Translucency scan with the radiology clinic.

The ultrasound clinics routinely forward their reports to SAMSAS. Once received, staff will combine the scan results with the serum biochemistry. You will receive a single report giving the aneuploidy risks calculated for the pregnancy.

View the First Trimester Screening NT Provider Progress Report 14 .

A single SAMSAS request form for the blood test is required.

Blood Test

1. Provide the patient with the SAMSAS pre-test information sheet
2. Use a SAMSAS request form (click link below to order SAMSAS request forms)
3. Complete ALL sections of the form
4. The test request is Second Trimester Screen
5. Refer patient to the Privacy Disclosure on the SAMSAS request form
6. If performing blood collection on site the sample type is 5-10 ml clotted blood sample (serum). Send the blood specimen to SA Pathology.

Completing the request form

For the best screening, careful documentation of the following factors is critical:

• Maternal weight: increased weight causes haemo-dilution, and it is greatly preferred that the patient be weighed, rather than weight estimated.
• Accurate gestational age: since biochemistry values are normalised for the given gestation, ultrasound data, if it exists, is preferred to clinical LMP.
• Maternal age: is included as a factor in the risk calculation algorithm.
• Age of egg donor: in IVF pregnancies, it is the age of the egg donor, mother or otherwise, that counts.
• Ethnicity: biochemical results can change based on different ethnicities.
• Pregnancy complications: factors such as smoking or insulin dependent diabetes are linked to different levels of serum analytes. For example, if a patient is a smoker, the PAPP-A will be lower. Since low PAPP-A is a marker for T21, if we are unaware that the patient is a smoker we could issue an incorrect higher risk.

Completing all the sections on the request form assists us in accurate calculation of risks and helps avoid unnecessary anxiety and/or invasive testing for the patient.

Reports

Important Note: please contact SAMSAS on 08 8161 7285 immediately if any risk calculation data should be different from that shown on the report.

Increased risk test results

The increased risk cut-off is 1 in 250. Any risk above this value is deemed increased risk (e.g. 1 in 200). Any risk below 1:250 is deemed not at increased risk (e.g. 1 in 1000). The risk is calculated for the date of blood collection.

Increased risk information sheets are provided with all increased risk reports issued by SAMSAS, and should assist the practitioner in communication with the affected family and with, if required, acquisition of diagnostic information.

Since this is a screening test and not diagnostic, some of the “Increased Risk” reports will be false positives, so that on subsequent diagnostic testing, a fetus may be found to have normal chromosomes. We calculate that only about one in 10 increased risk results will be confirmed on diagnostic confirmation at low probability levels like 1:200 or 1:250; however at higher probability levels especially over 1:50, the chance of abnormal chromosomes is much higher.

Low PAPP-A

Low PAPP-A in the absence of chromosomal abnormalities is the most common marker associated with adverse pregnancy outcomes. PAPP-A levels ≤0.37 MoM are below the 5^th centile. See below for further information.

Turn-around time

Once we have all the information we need, we can issue a report for first trimester screening within 1-2 business days and second trimester screening within 2-3 business days.

The most common cause of delay is awaiting gestational age, IVF information, or an NT scan report. Carefully filling out all sections of the request form initially assists in preventing delays.

Screen results are forwarded automatically to the requesting doctor. If you have not received a report in a timely manner, please call SAMSAS on 08 8161 7285.

Electronic reporting is available, please contact SAMSAS if required.

Costs

Patients will receive an account from SA Pathology. This account will be fully covered by Medicare.

For privately insured patients, SAMSAS continues its policy of accepting ‘Medicare only’ for the serum biochemistry analyses. There may be a gap payment for the ultrasound measurement. Check with the practice providing this service.

If SAMSAS has not been provided with an NT measurement from a scan report, or if the scan has not been performed within the required gestational ages, a suboptimal report will be issued. This report consists of a risk assessment calculated on biochemistry alone. An amended risk assessment will be issued upon the receipt of an NT measurement from the ultrasound provider.

The analyte AFP that is used for NTD is not discriminatory in the first trimester. It only becomes a useful marker at >14 weeks gestation.

Trisomy 21 (Down syndrome) and T18 (Edwards syndrome) are the most common aneuploidies in pregnancy. Some aneuploidies share the same analyte pattern as T18, but are much rarer. For example, the incidence for T18 is 1 in 10,000 live births, whereas for T13 it’s 1 in 20,000 live births. As T18 is the most likely diagnosis, we only report for this, but a high risk for T18 may lead to diagnosis of other aneuploidies.

We may also detect an abnormal analyte pattern in conjunction with a low risk for aneuploidy. This will be commented on in the individual report.

When the blood and scan are done on different days, the gestational age when the blood was collected is used in the risk generation assessment.

In line with RANZCOG guidelines and international best practice, SAMSAS uses the CRL measurement to date the pregnancy. SAMSAS uses a population specific equation for establishing estimated gestational age for a given CRL.

If the patient is >20 weeks 6 days, then a detailed ultrasound examination of the foetus is recommended as an alternative screening strategy.

No. Median values for our population have been established on our own instrument and they are not transferable to values from another instrument from another laboratory.

Where one fetus of a twin pregnancy has demised, biochemistry will remain biased by markers from the demised twin for up to 4 – 6 weeks. Since the date of demise of the twin is usually unknown, SAMSAS will calculate a risk based on NT and maternal age alone, in line with the ISUOG guidelines.

Because the levels of the biochemistry analytes change with gestational age (days) during the pregnancy, it would be difficult and confusing to report with reference ranges. To overcome this, the median value of an analyte is calculated for each gestational day of a pregnancy and a patient’s biochemistry values are divided by these medians to generate MoM values – “multiples of the median”. Therefore a MoM of 1 means the patient result is exactly on the median. A MoM of 0.5 means the patient result is half the median. A MoM of 2 means the patient result is double the median.

For more information see: Prenatal screening and diagnostic testing for fetal chromosomal and genetic conditions.

SAMSAS supports the practitioner-patient relationship, and believes that patient trust in this relationship is best upheld by communication remaining directly between practitioner and patient.

Additionally, laboratory staff are not clinically trained and do not have access to all the clinical information. Therefore, it is laboratory policy not to contact the patient.

Specific request forms are necessary for this type of service, as they name the information required. This distinguishes aneuploidy screening from serology and other tests performed routinely during pregnancy. Our specific request forms have tick-boxes or spaces for the information required and are recommended to be used in conjunction with pre-test information for parents: “Screening for neural tube defects, Down syndrome and Trisomy 18”.

Access request form.

Please call SAMSAS on 08 8161 7285 or email samsas.program@sa.gov.au for new request form pads. Please provide us with the doctor’s details (provider number, name, and address). We can also send pads of the pre-test information sheets for patients. This sheet is provided to facilitate pre-test counselling about screening.

• Increased risk of neural tube defect
• Increased risk of Down Syndrome
• Increased risk of Trisomy 18

• Spina bifida (healthdirect Australia)
• Hydrocephalus (healthdirect Australia)
• Down Syndrome SA
• Second Trimester Screening (14 weeks to 20 weeks)

Prenatal screening and diagnostic testing for fetal chromosomal and genetic conditions RANZCOG reviewed Jul 18

Newsletters

Earlier updates and reports are available upon request. Please contact us if you require copies of reports not available here.

• Update 16 – January 2017
• Update 15 – August 2009 Revised Age Specific Performance Data and Counselling Aid
• Update 14 – March 2009 Changes to Maternal Serum Screening

Nuchal translucency progress reports

• Nuchal translucency progress report 14 – 2019
• Nuchal translucency progress report 12 – January 2013
• Nuchal translucency progress report 11 – January 2012
• Nuchal translucency progress report 10 – November 2010

Birth defects register reports

• Prenatal Screening for Congenital Anomalies 2013 (published 2017)
• Birth Defects in South Australia 2016 – annual report (published 2020)
  
• Birth Defects in South Australia 2013 – annual report 2013 (published 2018)

• ADAM12 A promising new maternal serum marker in screening for Down syndrome in both first and second trimesters of pregnancy. View here.
  Robert Cocciolone, Renata Bird, Eva Martin, Diana Penhall, Lyn Raniolo (HGSA ASM, Adelaide SA, August 2008)
• Combining first and second trimester markers for Down syndrome screening: Think twice. Robert Cocciolone, Kate Brameld, Peter O'Leary, Eric Haan, Peter Muller, Karen Shand Aust N Z J Obstet Gynaecol 2008; 48: 492-500. View here.
  The definitive version of this paper is available at: http://www3.interscience.wiley.com/cgi-bin/fulltext/121476797/PDFSTART
• Trends in state/population-based Down syndrome screening and invasive prenatal testing with the introduction of first-trimester combined Down syndrome screening, South Australia, 1995-2005. Muller PR, Cocciolone R, Haan EA, et al Am J Obstet Gynecol 2007;196:315.e1-315.e7. View editorial and paper.
  
• Karyotypes found in the population declared at increased risk of Down syndrome following maternal serum screening. Richard G. Ryall et al. Prenatal Diagnosis 2001; 21: 553-557. View here.
• The impact of maternal serum screening on the birth prevalence of Down’s syndrome and the use of amniocentesis and chorionic villus sampling in South Australia. Tracy Cheffins et al. British Journal of Obstetrics and Gynaecology December 2000, Vol 107, pp. 1453-1459.
• Improved performance in a prenatal screening programme for Down syndrome incorporating serum-free hCG subunit analyses. R.G. Ryall et al. Prenatal Diagnosis, Vol. 12, 251-261 (1992)
• Epidemiology of Down syndrome in South Australia, 1960-89. Alan J. Staples et al. Am. J. Hum. Genet. 49:1014-1024, 1991