The AFP triple test or the Quad test is a screening test which is taken by a woman in the second trimester of her pregnancy. AFP test simply evaluates the health of the developing baby and the likelihood of development of any abnormalities. This test can usually predict your unborn child’s likelihood of developing abnormalities like Downs Syndrome, anencephaly, and neural tube defects.
Theses tests are known as the triple or quad tests because three or four of these tests are done together. They are most powerful when they are used together. When used in isolation, their accuracy may not be completely trusted. In these tests, the hCG, AFP, unconjugated estriol and inhibin A levels are measured. Other considerations like the race, age and health conditions of the parents are accounted for to predict chromosomal abnormalities and potential risk of birth defects.
The test results are a numeric value, which are then measured against a cut off. If the value of the test is above the cut off, it is considered a positive test. The AFP test may be ordered between the fifteenth and the twentieth week of the pregnancy.
The test is interpreted by a clinician or a practicing genetic counselor. Since the test results are numeric, they are simply compared to a cut off. If your test result is higher than the cut off, there is a high likelihood that the baby will be born with abnormalities.
Your doctor will be able to offer suggestions on the follow up procedure. These tests can only indicate risk. However, they cannot and should not be used as a diagnosis of fetal abnormality. When a screen is positive, it is usually followed by more tests, intending to determine the presence of an abnormality, if any. Some of the follow up tests include high resolution ultrasounds, chromosome analysis, and amniocentesis.
Sometimes, a fetal abnormality may not yield a positive result. Also, there are very few women who deliver baby without abnormalities even after getting a positive triple screen test. This is because the test is not diagnostic but only indicative.
The risk of developing an abnormality depends to a large extent on the gestational age of the fetus. The results may be false if the gestational age of the fetus has not been taken into account. It is also difficult to calculate the risk of fetal abnormalities in multiple gestational pregnancies. For twins it is still possible to have a somewhat accurate calculation, but for multiple fetuses, it is not possible.