The Triple Test, or Triple Marker Test, is a prenatal screening performed during the second trimester, typically between 14.1 and 22 weeks of pregnancy. It measures levels of three substances in the mother's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and estriol. This test helps assess the risk of certain chromosomal abnormalities, such as Down syndrome (trisomy 21) and trisomy 18, as well as neural tube defects. It is non-invasive and provides risk estimates but not a definitive diagnosis.