Prenatest® Prenatal Screening Test

The Prenatest® prenatal screening test is designed to provide patient specific risk for trisomy 21 (Down syndrome) and trisomy 18. The Prenatest screen combines maternal blood protein measurements with the ultrasound measurements of the fluid accumulation behind the neck of the foetus (nuchal translucency) and the presence of the nasal bone. Depending on the result, our service includes the option of a non-invasive prenatal test free of charge before proceeding with an invasive diagnostic test.

What is the difference between the Prenatest® and Prenatest® Plus services?

The Prenatest® Prenatal Screening service determines the risk of carrying a fetus with trisomy 21 or 18. Patients with a high risk result will be offered the option of a non-invasive prenatal test free of charge. In the first trimester, the detection rate of trisomy 21 is 90-95%1 and the false-positive rate is less than 0.1%2.

When carried out during the second trimester of the pregnancy (between the 15th and 22nd week), the test detects 75% of trisomy 21 cases.3 At this stage of the pregnancy, the test consists of a blood analysis combined ideally with a fetal ultrasound that will determine the age of the foetus and will improve the accuracy of results.

The Prenatest® Plus Prenatal Screening service has an additional risk category (intermediate risk) to increase accuracy. Patients with intermediate risk or high risk results will be offered the option of a non-invasive prenatal test free of charge. The detection rate of trisomy 21 is greater than 98%4 and the false-positive rate is less than 0.1%2. Prenatest® Plus is only available in the first trimester of pregnancy.

What are the results?

Prenatest®

LOW RISK

The risk of having a fetus with trisomy 21 is lower than the established threshold value of 1/250. This does not guarantee that the fetus is not affected, but the risk is low.

HIGH RISK

The risk of having a fetus with trisomy 21 is greater than or equal to the established threshold value of 1/250. However, this does not necessarily mean that the fetus is affected. Before proceeding with an invasive diagnostic test, the patient has the option of undergoing a non-invasive prenatal test free of charge.

Prenatest® Plus

LOW RISK

The risk of having a fetus with trisomy 21 is lower than 1/2,500. This does not guarantee that the fetus is not affected, but the risk is low.

INTERMEDIATE RISK

The risk is between 1/2,500 and 1/251. While the result is not high risk, the Prenatest® Plus service includes the option of a non-invasive prenatal test free of charge if the patient wishes to pursue further testing.

HIGH RISK

The risk of having a fetus with trisomy 21 is greater than or equal to 1/250. However, this does not necessarily mean that the fetus is affected. Before proceeding with an invasive diagnostic test, the patient has the option of undergoing a non-invasive prenatal test free of charge.

Who should be screened?

Women age 35 and over and those with a previous child with Down syndrome are more likely to have a baby affected with Down syndrome. However, most cases of Down syndrome occur in women under age 35. Therefore, screening provides useful information for all pregnant patients.

At what gestational age should the test be performed?

The test should be performed between 11 weeks-1 day and 13 weeks-6 days of pregnancy. The test may also be carried out during the second trimester of the pregnancy, between the 15th and 22nd week (ideally between the 16th and 18th week). At this stage of the pregnancy, the test consists of a blood analysis of alpha-fetoprotein (AFP) and free Beta-hCG combined with a fetal ultrasound that will determine the age of the foetus. This 2nd trimester screening test is also useful in detecting open neural tube defects.

How is the test performed?

The test begins with an ultrasound examination between 11w1d and 13w6d gestation (CRL between 45 and 84 mm). CRL is measured for accurate pregnancy dating and nuchal translucency (NT) is measured. NT has been demonstrated to be a specific marker for chromosomal aneuploidy. The nasal bone can also be measured, which increases the accuracy of the test. At the time of the ultrasound exam a blood sample is collected via fingerstick and deposited on filter paper. The ultrasound data is entered onto the test requisition form and sent to Dynacare Next along with the dried blood sample.

Dynacare Next analyzes the blood sample for free Beta-hCG and Pregnancy Associated Plasma Protein-A (PAPP-A) in the 1st trimester. Patient specific risk for trisomy 21 and trisomy 18 is then calculated based on the patient's age, the foetus' nuchal translucency measurement, the presence or absence of the nasal bone, and the free Beta-hCG and PAPP-A measurements.

What are the advantages of the Prenatest® screening test?

  • It is the best choice for prenatal screening in the first trimester
  • It does not pose any danger to the mother or the fetus
  • It includes a free non-invasive prenatal test for high risk results, as well as for and intermediate risk results with the Prenatest® Plus service
  • It offers the highest detection rate and lowest false-positive rate of any first trimester screen on the market
  • It is available to pregnant women of all ages

1 Nikolaides, K.H., 2011.
2 Norton, M.E. et al., 2012.
3 Macri, J.N., et al., 1996.
4 Nikolaides, K.H. et al. 2014.

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