The Triple Screen

What is the Triple Screen?

The Triple Screen is a prenatal screening test used to screen women who may be at increased risk of having babies with genetic disorders such as Down’s Syndrome or Trisomy 18 or developmental abnormalities such as Spina Bifida or anencephaly.

What Do the Tests Measure?

The Triple Screen measures maternal blood levels of Alpha Fetoprotein (AFP), Human Chorionic Gonadotropin (hcG) a hormone produced by the placenta and an indicator of pregnancy,  and unconjugated estriol (uE3) an estrogen produced by both the fetus and the placenta.

What do abnormal or false positive results mean?

The Triple Screen is just that-a screening test for potential genetic or developmental abnormalities. In women who are at increased risk of having a child with genetic or developmental abnormalities, these tests are done to asses risk. The tests are not diagnostic of any abnormality. If a woman has the tests and they come back abnormal, it is typically recommended that she have a diagnostic test such as amniocentesis or chorionic villus sampling to definitively determine if there is something wrong with the fetus.

Here in lies the controversy with the AFP test alone, the Triple Screen and the Quad Screen. Once a test comes back abnormal, mother usually goes on to have a definitive, diagnostic test. The amniocentesis and chorionic villus sampling diagnostic tests increase a mother’s chances of miscarrying. For tests known to have  high false positive rates when babies are completely healthy, putting these babies at risk if unacceptable for many people. As a result, many couples shun all prenatal testing and opt to accept whatever the pregnancy brings. Other couples that undergo the screening tests and receive positive results opt to have a Level II or Physiologic Ultrasound. These high powered ultrasounds enable obstetricians and perinatologists to look closely at the fetus and to evaluate if there are any genetic or developmental abnormalities.

There are many factors that can contribute to abnormal test results including inaccurate dates of gestation, multiple gestation and maternal diabetes to name a few. Prenatal screening alone cannot be the sole determinant of what is going on with fetal development. If a prenatal screening test comes back positive, the results have to be considered in light of maternal age, health status, and other potential confounding variables.