This test is most often done between the 15th and 22nd weeks of the pregnancy. It is most accurate between the 16th and 18th weeks.
The test measures levels of 4 pregnancy hormones:
- Alpha-fetoprotein (AFP), a protein produced by the baby
- Human chorionic gonadotropin (hCG), a hormone produced in the placenta
- Unconjugated estriol (uE3), a form of the hormone estrogen produced in the fetus and the placenta
- Inhibin A, a hormone released by the placenta
If the test does not measure levels of inhibin A, it is called the triple screen test.
To determine the chance of your baby having a birth defect, the test also factors in: