Triple Screen

Understanding the second trimester triple or quad screen

The triple screen (also called the triple test or multiple marker screening) is a blood test used to measure the levels of three important chemicals in the blood of an expectant mother: AFP, hCG and estriol. Depending on your doctor, you may be offered the quad screen instead, which checks the levels of these three substances as well as inhibin-A, a type of protein which is produced by your ovaries and your placenta.

The triple screen or quad screen is done to screen for the possibility of genetic abnormalities or disorders in the fetus, which can sometimes be predicted based on the levels of these chemicals along with certain factors about the mother, such as her ethnicity and age. All pregnant women should be offered the triple screen or quad screen test as part of a full regimen of prenatal tests, and it is usually performed between the 16th and 18th week of pregnancy. It is especially recommended that you have a quad screen performed if you come from a family with a history of birth defects, are an insulin-dependent diabetic, are over age 35, or if you have been exposed to certain viruses or chemicals during your pregnancy.

What the Triple and Quad Screen Tests Look For

Your doctor will explain the test to you in detail before you take it, but here are the basics of what the triple (or quad) screen is all about:

  • Alpha fetoprotein (AFP): The AFP test checks for both high and low levels of this protein, which is produced by your growing baby's liver.
  • hCG: Human chorionic gonadotropin is a hormone specific to the blood of pregnant women (and it is the same hormone that a pregnancy test looks for to confirm you're carrying a baby). The screening looks for unusually high or unusually low levels of hCG.
  • Estriol: Produced both in the placenta and by your fetus, estriol is a hormone is the estrogen family. Like hCG, the screening checks for both high and low levels.
  • Inhibin-A: As mentioned, this is a protein produced in your ovaries and placenta; the quad screen looks for abnormally high levels of inhibin-A.

Triple Screen and Quad Screen Test Results

Abnormally high levels of alpha fetoprotein can suggest a possible neural tube defect. Low levels of AFP along with abnormal levels of the other three substances may indicate an increased risk of chromosomal disorders such as Down syndrome. Unexpected AFP test results can also mean that you are carrying multiples or that your pregnancy has been incorrectly dated.

Remember, this is only a screening. It is not a diagnostic test, and the results are only suggestive of the possibility of genetic disorders rather than confirmation of them. It's important to keep in mind that the triple screen test has a high rate of false positive results. If the results of the screening are abnormal, your doctor will recommend further tests to determine the health of your fetus.

Although the triple screen test poses no threat to either maternal or fetal health, a positive result can cause an expectant mother a lot of stress and may lead to more invasive tests. For this reason, some women choose not to have the test, especially if they are certain that they would want to carry a baby to term regardless of possible birth defects.