Prenatal Testing Can Yield Valuable Information

The maternal serum screen, or triple screen as it is also called, is a blood test performed around 16 weeks of pregnancy to help determine the risk of certain birth defects.

Three proteins made by the developing baby or placenta are measured: AFP (alpha fetoprotein), hCG (human chorionic gonadotropin) and VE3 (estriol).

These three proteins ar found in the amniotic fluid surrounding the baby, are capable of crossing the placenta and therefore, entering mom's bloodstream. A blood sample from the mother is all that is needed to detect the level of each of these proteins.

What is the significance of the level of these proteins? An elevated AFP level may indicate an opening on the baby's body. The opening may be in the spinal column, head, or the gastrointestinal wall. This screening test can detect 80% of all babies with these abnormalities. A depressed AFP level, particularly in combination with an elevated hCG, indicates an increased risk for Down syndrome. A depressed AFP level may also be indicative of other chromosome abnormalities such as trisomy 18. A depressed level of estriol may indicate a skin disorder or a defect in cholesterol metabolism in the developing baby.

An abnormal serum screen result is an indication for more specific testing of the pregnancy by amniocentesis or high resolution ultrasound.

Amniocentesis requires drawing a sample of the amniotic fluid surrounding the baby in order to perform biochemical, chromosome, or other genetic studies. This study is usually performed in the second trimester. The test is very definitive and can detect chromosomal abnormalities, (such as Down syndrome) defects of the spinal cord an brain, and many other disorders.

Amniocentesis is usually performed only when there is an increased risk for some abnormality in the baby.