Maternal Serum Screen

MATERNAL SERUM SCREEN / TRIPLE MARKER SCREEN

WHAT IS THE MATERNAL SERUM SCREEN?

MSS is a blood test offered to all pregnant women in British Columbia. It is also called the Triple Marker Screen (TMS). Maternal Serum Screening (MSS) is an optional screening test that estimates a woman’s risk of having a baby with Down syndrome, Open spina bifida, and Trisomy 18. The test can only be done between 15 and 20 weeks of pregnancy. It is very important to understand that Maternal Serum Screening is not a diagnostic test, and can only indicate if a pregnancy is at increased or decreased risk for any of the above conditions. Women who are found to be at increased risk are offered further diagnostic testing such as detailed ultrasound and/or amniocentesis. Not all affected pregnancies are detected by the MSS. MSS can detect approximately 75% of cases of Down Syndrome, 85% of Open Spina Bifida and 60% of Trisomy 18. The test is relatively painless and poses no risk to the mother or the pregnancy. Accurate dating of the pregnancy is essential for this test.

HOW IS THE MATERNAL SERUM SCREEN DONE AND WHAT DOES IT MEASURE?

Maternal Serum Screening is performed at any medical laboratory when the woman has the MSS test requisition that is fully completed by the midwife. A lab technician collects a sample of blood from the woman’s arm using a slender needle and a small collection vial. The procedure takes about 10 minutes. The sample of blood is tested for the levels of three proteins: alpha-fetoprotein (AFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG). These proteins are made by the baby or the placenta, and the levels are measured in the mother’s blood. The levels of these proteins are different than normal in some pregnancies affected with Down syndrome, Open spina bifida, or Trisomy 18. The levels of these three proteins, in combination with the woman’s age, weight and other factors are used to estimate the woman’s individual risk in this pregnancy. It takes 7-10 days for the results to become available.

WHAT ARE DOWN SYNDROME, OPEN SPINA BIFIDA AND TRISOMY 18?

Individuals with Down syndrome have an extra chromosome. The extra chromosome causes characteristic facial features, mental disability, and some other health concerns. Open spina bifida occurs when there is an opening in the spine causing nerve damage. The effect of an open spine is variable, depending on the size and location of the opening. Trisomy 18 is rare. Most babies with Trisomy 18 do not survive to delivery, or die shortly after birth. Babies with Trisomy 18 have severe mental disability and major physical problems. Please talk to your midwife or a genetic counsellor for more information about these conditions.

WHAT ARE THE RISKS OF THE MATERNAL SERUM SCREEN?

Maternal