Prenatest® Prenatal Screening Test

What is the Prenatest Prenatal Screening Test?

The Prenatest® Prenatal Screening Test is performed during your first trimester of pregnancy. It lets you know your risk of carrying a fetus that may be affected by one of the most common birth anomalies: trisomy 21 and trisomy 18. Quick and straightforward, the Prenatest® method requires a few drops of blood taken from the tip of your finger and a fetal ultrasound.

Performed early, in the first trimester, the Prenatest® screen will provide results rapidly to give you time to consider your options. This test does not provide a final diagnosis on the health of the fetus you are carrying. Depending on your risk result, our service includes the option of a non-invasive prenatal test free of charge before proceeding with an invasive diagnostic test.

The test is designed for all pregnant women, regardless of their age, and does not pose any danger to the mother or to the fetus. It is also available for twin pregnancies.

The Prenatest® prenatal screening service offers the highest level of accuracy for determining your risk of carrying a fetus with trisomy 21 or trisomy 18. We offer two options to provide higher accuracy and added value: Prenatest® and Prenatest® Plus.

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

The Prenatest® Prenatal Screening service will inform you of your 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.

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%3 and the false-positive rate is less than 0.1%2. Prenatest® Plus is only available in the first trimester of pregnancy.

Please refer to the Understanding Your Results section for more details on the results.

What is a screening test?

A screening test is different than most medical tests that are performed. Most medical tests are diagnostic and provide the doctor and patient with a definitive result. A diagnostic test shows that the patient either has a type of medical condition or does not have the condition. In a screening test, the result shows only the patient's risk or chance of having the medical condition. Patients who are at high risk may in fact not have the medical condition. The screening test is one of several factors that help patients decide whether they would like to undergo a definitive diagnostic test.

In the field of prenatal testing, screening is especially applicable since the diagnostic tests for trisomy 21 and trisomy 18 (chorionic villus sampling or amniocentesis) can cause pregnancy complications or in some cases a miscarriage. Therefore, it is not practical to provide diagnostic testing to all pregnant women. By performing the screening test first, patients are provided with a risk that their pregnancy may be associated with trisomy 21 or trisomy 18. Depending on the patient's risk, they may have the option of a non-invasive prenatal test free of charge before proceeding with an invasive diagnostic test. If the risk of this test is high, patients may then decide that they are interested in a more definitive result by undergoing the diagnostic test. It is important to remember, however, that most patients with an elevated risk from the screening test will not be diagnosed as having a pregnancy associated with trisomy 21 or trisomy 18. The vast majority of such patients give birth to a healthy child.

How is the Prenatest® screening test performed?

The Prenatest® method includes a simple blood test and a prenatal ultrasound.

A simple blood sampling is performed by pricking your finger and applying drops of blood to a specific type of paper. The blood sample is analyzed for two chemicals called free Beta-human chorionic gonadotropin (hCG) and pregnancy associated plasma protein-A (PAPP-A), which are normally found in the blood of all pregnant women.

The prenatal ultrasound is used during the first trimester your pregnancy, to assist your doctor in determining:

  • the viability of the fetus
  • the size of the fetus and estimate the gestational age
  • the presence of more than one fetus
  • some fetal abnormalities

Ultrasound utilizes sound waves to take a picture of your fetus. During the first trimester, special ultrasonographic measurements can be made. The nuchal translucency (NT), the amount of fluid accumulation at the back of the fetal neck, and the presence of the nasal bone can also be accurately measured between 11 weeks-1 day and 13 weeks-6 days of your pregnancy.

The results of the blood test will be combined with the results of the ultrasound exam to establish a specific risk for trisomy 21 and trisomy 18.

Who can be tested?

Pregnant patients of any age can be tested.

Women age 35 and over and those with a previous child with a trisomy are more likely to have a baby affected with a trisomy, therefore many physicians offer their patients the opportunity to undergo a diagnostic test (chorionic villus sampling or amniocentesis). However, since these diagnostic tests are associated with an increased risk of miscarriage of about 1%4, many patients prefer to wait and learn their risk of trisomy 21 and trisomy 18 through the Prenatest® screening test prior to deciding whether to undergo diagnostic testing.

Women under age 35 may want to perform the test since most cases of trisomy 21 occur in this age group.

When can I get tested?

The Prenatest® Screening Test should be performed during the first trimester, between the 11th and 14th weeks of your pregnancy.

If you consult your doctor at a later date, a second trimester Prenatest® screen can be performed between the 15th and 22nd weeks of pregnancy. This second trimester screening test is also useful in detecting open neural tube defects. In the second trimester, the test requires a blood draw to measure 4 chemicals: AFP, free beta-hCG, uE3, and Inhibin-A.

When do I get the results?

Results of the Prenatest® Prenatal Screening test are provided within 3 business days once the laboratory receives the sample. If the patient is eligible for a free non-invasive prenatal test, the results of this test are provided within 10 business days.

1Nikolaides, K.H., 2011.
2Norton, M.E. et al., 2012.
3Nikolaides, K.H. et al. 2014.
4Alfirevic, Z. et al. 2003.