Triple Test: AFP Plus (Multiple Marker Screening)

The triple test is a maternal blood screening test that looks for three specific substances: AFP, hCG, and Estriol.

  • AFP: alpha-fetoprotein is a protein that is normally produced by the fetus.
  • hCG: human chorionic gonadotropin is a hormone produced within the placenta
  • Estriol: estriol is an estrogen produced by both the fetus and the placenta

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:

  • Have a family history of birth defects
  • Are 35 years or older
  • Used possible harmful medications or drugs during pregnancy
  • Have diabetes and use insulin
  • Had a viral infection during pregnancy
  • Have been exposed to high levels of radiation

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:

  • Defects in the ventral wall of the baby
  • Defects in the digestive system of the baby
  • Women carrying twins
  • Pregnancies that are more or less advanced than thought
  • Risks of premature birth, preeclampsia and miscarriage

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
Down Syndrome Low Low High
Trisomy 13 Normal No Data Low
Trisomy 18 Low Low Low
Open Neural Tube Defects High Normal Normal
IUGR, preterm birth, stillbirth High No Data No Data
Multiple Gestation High High High

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.