The triple test is a maternal blood screening test that looks for three specific substances: AFP, hCG, and Estriol.
It is a non-invasive procedure done through a blood test with little to no risk to the mother or developing baby.
How is the triple test performed?
The triple test involves drawing blood from the mother which takes about 5 to 10 minutes. The blood sample is then sent to the laboratory for testing. The results usually take a few days to receive.
What are the risks and side effects to the mother or baby?
Except for the discomfort of drawing blood, there are no risks or side effects associated with the triple test.
When is the triple test performed?
The triple test is performed between the 15th and 17th week of pregnancy. Accurate results can still be obtained through 20 weeks gestation; in rare cases it may be performed up to 22 weeks.
All pregnant women should be offered MSAFP screening, but it is recommended for women who:
What does the triple test look for?
The triple test is measuring high and low levels of AFP and abnormal levels of hCG and estriol. The results are combined with the mother's age and ethnicity in order to assess probabilities of potential genetic disorders.
High levels of AFP may suggest that the developing baby has a neural tube defect. The most common neural tube defects are spina bifida and anencephaly.
Low levels of AFP may indicate that the developing baby has Down syndrome (Trisomy 21).
Abnormal levels of hCG and estriol may indicate that the developing baby may have chromosome abnormalities.
Although the primary reason for conducting the triple test is to screen for genetic disorders, the triple test has also been used to identify:
What do the triple test results mean?
It is important to remember that the triple test is a screening test and not a diagnostic test. This test only notes that a mother is at risk of carrying a baby with a genetic disorder. Many women who experience an abnormal test discover later that the test proved false.
The results for AFP, estriol and hCG levels are usually phrased as high or low values. For example, the combination of a low AFP, low estriol and a high hCG suggests further screening for Down Syndrome. The following table presents the potential assessment associated with different score combinations:
|Triple Test Values|
|Trisomy 13||Normal||No Data||Low|
|Open Neural Tube Defects||High||Normal||Normal|
|IUGR, preterm birth, stillbirth||High||No Data||No Data|
Abnormal test results warrant additional testing for making a diagnosis. A more conservative approach involves performing a second triple test followed by a high definition ultrasound. If the testing still maintains abnormal results, the more invasive procedures such as amniocentesis or CVS, may be performed.