Maternal Serum Prenatal Screening (MSPS): A Choice During Pregnancy

Please note that if you have had the First Trimester Combined Screening, we currently do not advise that you have this screen.

What is the Maternal Serum Prenatal Screen (MSPS) or Triple Screen?

The MSPS is a blood test available to all pregnant women between 15-20 weeks of pregnancy (counting from the first day of the last menstrual period). The test can identify pregnancies at an increased risk for Down syndrome, Trisomy 18, and Neural Tube Defects.

Why is it called a screening test?

• Some pregnancies will be identified as being in the increased risk group even though the baby is not affected.
• A small number of babies with Down syndrome, Trisomy 18, or a Neural Tube Defect will not be identified because a screening test cannot detect all affected pregnancies.
• The MSPS test cannot detect all health concerns or birth defects.

What does the MSPS involve?

You will have a blood sample drawn between 15-20 weeks gestation. An ultrasound may be needed before the blood test if you are unsure of how far along you are.Three substances that are naturally made be either the baby or the placenta (baby’s support system) are measured. These are called alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3). The test result is also based on specific information about you. This includes your age, weight, race, if you have diabetes, and the number of babies in this pregnancy (example: twins).

The amounts of these substances are used to calculate a woman’s specific risk in this pregnancy for Down syndrome, Trisomy 18, and Neural Tube Defects.

What are Chromosome conditions and Neural Tube Defects?

Please see Understanding Chromosome Conditions  web page for this information. 

What type of results should I expect from the MSPS?

The results of the MSPS are sent to your doctor and are usually available within a week.

A cut-off of 1 in 385 is used with this screen. Using this cut-off, there are two possible screen results for each condition, either a “screen positive” or a “screen negative”. 

• A “screen negative” result means that the chance of having a baby with one of these three conditions is low (below the cut-off). Follow-up tests, aside from the option of 18 week ultrasound are not needed unless there are other reasons. 
• A “screen positive” result means that the chance of having a baby with one of these conditions is above the cut-off. More testing may be offered. A screen positive result does not mean that the baby has a health concern.

What follow-up testing might be suggested?

Genetic counselling may be suggested in order to answer your questions about the MSPS result. Genetic counsellors also explain about the benefits and limitations of further testing that may be offered and help you decide about further tests.

Ultrasound may be offered. This is a procedure where sound waves are used to create a picture of the baby on a screen. It may be used to confirm the age of the baby. It can also be used to detect most Neural Tube Defects and some other birth defects. Down syndrome and Trisomy 18 cannot be diagnosed through ultrasound.

Amniocentesis may be offered. This is a procedure done to test and diagnose chromosome problems like Down syndrome and Trisomy 18. Amniocentesis tests the cells in the amniotic fluid (the water around the baby inside the mother). The fluid can also be used to test for Neural Tube Defects in the baby. This test cannot tell how mild or severe the condition will be.There are risks associated with having an amniocentesis that are explained to you in counselling to assist you in making a decision about testing.

How accurate is MSPS?

MSPS does not detect all babies with these conditions. The detection rate is about 70% for Down syndrome and Trisomy 18 and 80% for spina bifida. This means that 70% of women carrying a baby with Down syndrome or Trisomy 18 will be identified with a screen positive result and 80% of women carrying a baby with spina bifid will be identified with a positive result.

MSPS does not screen for other conditions.

Important things to remember about MSPS

• It is your choice whether you want to have this test or any follow-up tests that may be offered during your pregnancy.
• A healthy baby and normal pregnancy are still most likely, even after a positive MSPS result.
• This test detects most pregnancies at an increased risk for Down syndrome, Trisomy 18 and Neural Tube Defects.
• Genetic counsellors are available to answer your questions.

For more information contact the Prenatal Genetics Clinic in Calgary at (403) 943-8375